LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


POWER 


AND 


POWER  TRANSMISSION. 


BY 

E.     W.     KERR,     M.E., 

Professor  of  Mechanical  Engineering,   Louisiana  State  University. 


SECOND   EDITION,  REVISED. 
SECOND   THOUSAND. 


NEW  YORK: 
JOHN   WILEY   &  SONS. 

LONDON:    CHAPMAN  &   HALL,   LIMITED. 

1908. 


Copyright,  1902,  1908 

BY 

E.  W.  KERR. 


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PREFACE. 


THE  matter  contained  in  the  following  pages  is  largely  the 
subject-matter  of  lectures  delivered  by  the  author  to  students 
of  the  elementary  principles  of  engineering. 

The  author  does  not  and  could  not  presume  to  have  pre- 
sented much  that  is  new,  but  rather  a  collection  of  such 
principles  and  information  as  would  direct  the  beginner  along 
the  proper  course  of  study. 

In  preparing  the  work  free  recourse  has  been  had  to  various 
works  upon  the  subjects  named,  from  which  much  subject- 
matter  has  been  used. 

It  is  not  intended  that  the  subjects  treated  should  be 
regarded  by  the  student  as  exhausted,  but  rather  as  containing 
guiding  principles  for  more  thorough  investigation,  either  in 
the  classroom  or  in  practice. 

The  problems  at  the  end  of  the  different  chapters  are  given 
more  for  the  purpose  of  fixing  in  the  mind  of  the  student  the 
more  important  principles  contained,  than  as  examples  of 
practice,  though  in  fact  many  of  them  are  such. 

To  Prof.  R.  H.  Whitlock,  whose  assistance  and  encourage- 
ment are  largely  responsible  for  the  undertaking  of  the  prepara- 
tion of  this  work,  and  under  whom  he  has  studied  for  several 
years,  the  author  wishes  to  render  thanks. 

To  Prof.  Chas.  Puryear  thanks  are  due  for  assistance  in 
reading  proof. 

The  author  is  under  obligations  to  the  various  manufac- 
turers who  have  loaned  electrotypes." 

iii 


196445 


IV  PREFACE. 

Figures  34,  35,  36,  37,  41,  42,  73,  74,  76,  78,  89,  90, 
91,  92,  96,  97,  from  Robinson's  "Principles  of  Mechanism," 
Figures  123,  138,  139,  150,  from  Kinealy's  "Steam  Engines 
and  Boilers,"  Figures  158,  179,  180,  181,  from  Whitham's 
"Constructive  Steam  Engineering,"  and  Figures  121,  132, 
171,  173,  175,  182,  183,  191,  192,  197,  198,  from  Mutton's 
"  Mechanical  Engineering  of  Power  Plants,"  and  the  electros 
for  the  same,  were  used  by  the  permission  of  the  authors  of 
those  works,  for  which  the  writer  is  indebted. 

E.  W.  KERR, 

COLLEGE  STATION,  TEXAS, 
Nov.  29,  1901. 


PREFACE   TO   THE    SECOND   EDITION. 


THE  book  has  been  improved  by  rewriting  the  chapters  on 
Steam  Turbines  and  Valve  Diagrams,  also  by  the  addition  of 
several  pages  of  matter  upon  the  subject  of  heat  and  the  use 
of  the  steam  table,  at  the  beginning  of  the  chapter  upon  steam 
boilers.  The  steam  table  of  the  old  edition  has  been  replaced 
by  another  one,  more  complete  and  better  adapted  to  the  solu- 
tion of  problems. 

A  large  number  of  good  problems  have  been  added  and  a 
thorough  correction  of  errors  made  throughout  the  book.  The 
present  edition  contains  175  problems  and  ten  pages  more 

matter  than  the  former  edition. 

E.  W.  K. 

BATAN  ROUGE,  LA.,  December  29,  1907. 


CONTENTS. 

PART  I.     MACHINERY   AND   MECHANICS. 

CHAPTER  I. 

PAGE 

INTRODUCTION    I 

Definition  of  terms,  i.  Mechanics,  Force,  Analysis  of  a  Ma- 
chine, 2.  Simple  Machines,  Classification  of  Levers,  3.  Law  of 
Machines,  Inclined  Plane,  4.  Wedge,  6.  Screw,  Cam,  Pulley  or 
Block,  7.  Wheel  and  Axle,  Energy,  Work,  Power,  etc.,  10. 
Conservation  of  Energy,  n.  Sources  of  Energy,  12.  Work,  Ef- 
ficiency, 13.  Power,  14.  Problems,  14. 

CHAPTER  II. 

SHAFTING  16 

Description  of  different  kinds  of  Shafting,  16.  Materials  and 
manner  of  making,  17.  Strains  of  Shafting,  Collars,  18.  Speed, 
19.  Formulas  for  Diameter  of  Shafting,  20.  Couplings,  21. 
Friction-clutch,  22.  Work  transmitted  by  a  Shaft,  23.  Prony 
Brakes,  24. 

CHAPTER    III. 

BEARINGS    26 

Classification,  26.  Ball  and  Roller  Bearings,  29.  Dimensions 
of  Bearings,  30.  Bearing-surface,  Methods  of  applying  Oil  to 
Bearings,  30.  Problems,  32. 

CHAPTER    IV. 

FRICTION  AND  LUBRICATION  OF  BEARINGS  '. 34 

Friction,  Coefficient  of  Friction,  34.  Angle  of  Repose,  Morin's 
Laws  of  Friction,  35.  Laws  of  Friction  (Goodman),  36.  Friction 
of  different  Metals  upon  each  other,  37.  Cast-iron  as  Bearing 
Metal,  Babbitt,  38.  Qualities  of  good  Lubricants,  39.  Lubricants 
for  different  conditions  of  practice,  Graphite,  40. 

vii 


viii  CONTENTS. 

CHAPTER  V. 

PAGE 

FRICTION  WHEELS  41 

Materials  used  in  making,  Advantages  and  Disadvantages  of, 
41.  For  Parallel  Shafts,  42.  For  Shafts  not  Parallel,  43.  Graphi- 
cal Methods,  44.  Equation  of,  45.  Problems,  45. 


CHAPTER    VI. 

PULLEYS    47 

Classification,  Materials  of  Construction,  Manner  of  fastening  to 
Shaft,  47.  Different  kinds  for  different  uses,  49.  Design  of  Cone 
Pulleys,  52.  Problems,  52. 

CHAPTER  VII. 

BELT  GEARING 54 

Leather  and  Rubber  Belts,  54.  Best  working  of  Belts,  55.  For- 
mulas for  H.P.,  56.  Rubber  Belts,  57.  Strength  of  Belting,  58. 
Lacing,  59.  Rope-driving,  Advantages  of,  61.  H.P.  of  Rope- 
drive,  63.  Problems,  64. 


CHAPTER  VIII. 

TOOTHED  WHEELS  66 

Certain  transmission  of  Toothed  Wheels,  Advantages  and  Dis- 
advantages of,  as  compared  with  Belt  transmission,  Similarity  to 
Friction  Wheels,  66.  Proportion  of  parts  of  Gear-wheel,  67. 
Spur-wheels,  Bevel-wheels,  Skew-wheels,  Form  of  Teeth,  Ma- 
chines for  making  Gears,  Cast  and  Cut  Gears,  68.  Wooden 
Teeth,  manner  of  representing  Teeth,  Clearance,  Back-lash,  69. 
Dimension  of  a  Gear-wheel,  70.  Annular  Gear,  Pinion,  Rack,  71. 
Equations  of  Speed,  System  of  Gear-wheels,  Train  of  Gear-wheels, 
72.  H.P.  of  Gear-teeth,  73.  Problems,  74. 


CHAPTER  IX. 

THE  SCREW  75 

Efficiency  of  the  Screw,  Jack-screw,  Equation  of,  75.  Endless 
Screw,  76.  Equation  of  Endless  Screw,  Angular  Velocity,  77. 
Screw-threads,  U.  S.  Standard  Thread,  Flat  of,  Table  of,  78. 
Whitworth  Thread,  Square  Thread,  Male,  Female,  79.  Manner  of 
making  Screw-threads,  Bolts,  Machine-bolts,  Carriage-bolt,  Stove- 
bolt,  80.  Cotter-bolt,  Stove-bolt,  Stud,  Screws,  Cap-screws,  Lag- 
screw,  81.  Drive-screw,  Wood-screw,  Problems,  82. 


CONTENTS.  ix 

CHAPTER  X. 

PAGE 

CAMS  84 

Use  of  Cams,  Friction  and  Wear  of  Cams,  85.  Path  of  Follower, 
Swinging  Follower,  Flat-foot  Follower,  Curve  of  Cam  in  which 
Velocity  Ratio  of  Rod  and  Axis  are  constant,  86.  Spiral  of  Archi- 
medes, 87.  Cam  for  Variable  Velocity  of  Revolution,  Cams  for 
Valve  Moments,  Shear  operated  by  Cam,  Inverse  Cam,  88.  Rela- 
tion of  Applied  Force  to  Resistance,  89. 

CHAPTER  XI. 

THE  LEVER  AND  SOME  OF  ITS  MODIFICATIONS  90 

Examples  of  Levers,  Law  of  the  Lever,  90.  Rack  and  Pinion, 
Moving  Strut,  Toggle-joint,  91.  Wheel-work,  Cranes,  etc.,  Prin- 
ciple of  Wheel-work,  -Law  of  Wheel-work,  92.  Block  or  Pulley, 
Differential  Windlass,  93.  Equation  of  Work  for  Differential 
Windlass,  94.  Differential  Pulley,  Hoists,  95.  Problems,  96. 

CHAPTER  XII. 
LINK   WORK   98 

Applications  of  Link-work,  Advantages  of  Link-work,  98. 
Paths  of  various  Points  of  Link-wrork,  100.  Equivalents  for  Link- 
work,  Dead-points,  Dead-center,  101.  Manner  of  providing 
against  Dead-points,  102.  Conical  Link-work,  103.  Hooke's  Uni- 
versal Joint,  104. 

CHAPTER  XIII. 

PIPE   FITTINGS   105 

Valves,  Different  Classes  of,  Globe-valve,  105.  Gate-valve, 
Check-valve,  106.  Throttle-valve,  Valve-regrinder,  107.  Slide- 
valve,  Poppet-valve,  Back-pressure  Valve,  108.  Regulating-valve, 
109.  Piping,  no.  Fittings,  in. 


PART   II.     STEAM-POWER. 

CHAPTER  XIV. 

HEAT    AND   STEAM    112 

Heat,  Temperature,  Absolute  Temperature,  Pressure,  Absolute 
Pressure,  112.  Steam,  Effects  produced  by  applying  Heat  to 
Water  and  Steam,  different  kinds  of  Steam,  Calculation  of  Heat 


CONTENTS. 

p 

in  Steam,  114.  Plant  for  producing  Steam,  Manner  of  producing 
Steam,  Furnace,  Chimney,  Boiler,  116.  Classes  of  Boilers,  Fire- 
tube  Boilers,  Water-space,  Steam-space,  Manner  of  providing  for 
Dry  Steam,  Heating-surface,  117.  Formula  for  Heating-surface, 
Tubes,  Flues,  Internally-fired  Boilers,  120.  Cornish  Boiler,  Loco- 
motive Boiler,  Water-tube  Boilers,  121.  Scotch  Boiler,  122. 
Header,  Babcock  and  Wilcox  Boiler,  124.  Heine  Boiler,  Stirling 
Boiler,  125.  Water-tube  Boilers,  Safety  Boilers,  Heating-surface 
of  Water-tube  Boilers,  Boiler-setting,  126.  Setting  for  Return 
Tubular  Boiler,  Double  Wa'ls,  Grate-surface,  128.  Bridge-wall, 
Ash-pit,  FJame-bed,  129.  Cleaning-door,  Hanging  the  Boiler,  Two 
Methods  of,  130.  Force  of  Draft,  Measuring  the  Draft,  Formulas 
for  Height  of  Chimney,  132.  Chimneys,  Position  of  Stack  for 
different  Boilers,  Brick  Chimney,  Steel  or  Wrought  Iron  Chim- 
neys, 131.  Breeching.  Forced  Draft,  Manner  of  Producing, 
Blower,  133.  Chimney  for  Forced  Draft,  134.  Combustion,  Rate 
of  Combustion,  Maximum  and  Minimum  Rate,  Principal  Elements 
in  Fuels,  135.  Heat-units  in  a  pound  of  Fuel,  Total  Heat  required 
to  be  generated,  136.  Air  required  for  Combustion,  Fuels,  Wood, 
Coal,  Petroleum,  Table  of  Fuels  with  their  Heating-power,  137. 
Coke,  Roney  Stoker,  Petroleum  Fuel,  Manner  of  Firing  Petro- 
leum, 139.  Plant  for  Burning  Petroleum  Fuel,  141.  BoiLr  Acces- 
sories, Steam-gauge,  Water-gauge,  142.  Gauge-cocks,  Water- 
column,  Safety-valve,  Formula  for  Safety-valve,  143.  Feed- 
water,  144.  Feed-pump,  Injector,  146.  Feed-water  Heater,  147. 
Feed-pipe,  Economizer,  Blow-off  Pipe,  148.  Blow-off  Valve, 
Dampers,  Problems,  151. 


CHAPTER   XV. 

SIMPLE  STEAM-ENGINE 154 

Reciprocating  and  Rotary  Steam-engines,  Multiple-expansion 
Engine,  Compound  Engine,  154.  Condensing,  Non-condensing, 
Single-acting,  Double-acting,  Cylinder,  Piston,  Piston-rings, 
Steam-chest,  D  Valve,  155.  Eccentric,  156.  Expansion  of  Steam 
according  to  Marriotte's  Law,  Points  of  Cut-off,  Release,  Admis- 
sion, Compression,  Formula  for  Thickness  of  Cylinder-walls,  158. 
Cylinder-head,  Piston,  Built-up  Piston,  Piston-rod,  Formula  for 
Diameter  of,  159.  Cross-head,  160.  Cross-head  Pin,  Dimensions 
of,  161.  Guides,  Formula  for  Area  of  Slides,  Connecting  Rod, 
Formula  for  Diameter  of,  162.  Connecting  rod  Brasses,  Crank, 
163.  Crank  pin,  Diameter  of,  164.  Length  of  Crank-pin,  Crank- 
shaft, Diameter  of,  Crank-shaft  for  Armature  of  Direct-connected 
Dynamo,  Fly-wheel,  Diameter  of,  166.  Eccentric,  Eccentricity, 
Eccentric-strap,  Eccentric- rod,  Valve- rod,  Diameter  of  Valve-rod, 


CONTENTS.  xi 

PAGE 

Steam-chest,  Form  of  Steam-chest,  Openings  in  Steam-chest,  167. 
Steam-ports,  Area  of,  Bridge,  Exhaust-port,  Exhaust-pipe,  Bed  of 
Engine,  Regulation  of  Speed  of  Engine,  168.  Throttling  Gov- 
ernor, Clearance,  Back-pressure,  Stroke,  Velocity  of  Piston,  170. 
Problems,  171. 

CHAPTER  XVI. 

AUTOMATIC  CUT-OFF  ENGINES.     HIGH-SPEED  ENGINES  173 

Long-stroke  and  Short-stroke  Engines,  Regulation  by  changing 
Travel  of  Valve,  High  Rotative  Speed  of,  Greatest  Source  of 
trouble  with,  173.  Clearance,  Balanced  and  Multiple-ported 
Valves,  Piston-valve,  Governor,  175.  Corliss  Engine,  Valves, 
High  Piston-speed,  Long  Stroke,  177.  Clearance,  Speed,  Perfect 
Control  of,  179.  Back-pressure,  Economical  in  the  use  of  Steam, 
High  First  Cost,  Arrangement  of  Valves,  180. 


CHAPTER  XVII. 

INDICATORS 181 

Use  of,  Indicator-card,  Mechanism  of  Indicator,  Operation,  181. 
Atmosphere  Line,  182.  Springs,  Conditions  required  in  a  good 
Indicator,  Method  of  taking  Cards  from  both  ends  of  Cylinder  at 
one,  Reducing  Motions,  183.  Length  of  Card,  Pendulum  Reduc- 
ing Motion,  Pantograph,  185.  Taking  the  Card,  Data  for  Card, 
Typical  Card,  186.  Finding  Average  Height,  Mean  Effective 
Pressure,  H.P.  from  Indicator  Card,  187.  Weight  of  Steam  per 
Hr.  per  H.P.  calculated  from  Card,  188.  Construction  of  Theo- 
retical Expansion-line,  Clearance-ratio  to  find,  Vacuum-line,  190. 
Cards  showing  improper  working  of  Valves,  191.  Thermal  Effici- 
ency, 192.  Commercial  Efficiency,  Performance  of  Engines  in 
Practice,  Problems,  193. 


CHAPTER  XVIII. 

'COMPOUND  ENGINES 196 

Compounding,  High-  and  Low-pressure  Cylinders,  196.  Stages 
of  Expansion,  Tandem  and  Cross-compound,  1973.  Cross-com- 
pound, advantages  of,  198.  Simple  and  Compound  Engines  com- 
pared, Losses  in  Engines,  Advantages  of  Compounding,  198. 
Range  of  Temperature  in  Cylinder,  Objections  to  Compounding, 
199.  Ratio  of  Cylinders,  Receiver,  Receiver-space,  200.  Indica- 
tor-card, 201.  Problem,  Combining  Indicator-cards  of  a  Com- 
pound Engine,  202.  Theoretical  and  Actual  Work  from  Card,  205. 


xii  CONTENTS. 

CHAPTER  XIX. 

PAGE 

CONDENSERS 206 

Principle  of,  206.  Jet-  and  Surface-condensers,  207.  Wheeler 
Condenser,  208.  Worthington  Condenser,  209.  Jet-  and  Surface- 
condensers  compared,  210.  Manner  of  cooling  Condenser  water, 
2H.  Condenser-plant,  212.  Condenser  Tube-joints,  213.  Air- 
pump,  Belt-driven  and  Independent  Condensers,  214.  Vacuum- 
gauge,  215.  Siphon  Condenser,  Indicator-card,  Problems,  217. 

CHAPTER  XX. 

VALVES  AND  VALVE-GEARING 218 

D  Slide-valve,  Steam-lap,  Exhaust-lap,  218.  Lead,  Manner  of 
changing  Lead,  219.  Effect  of  Steam-  and  Exhaust-lap,  220. 
Setting  an  Eccentric,  Locating  the  Engine  on  the  Center,  Revers- 
ing-gears,  221.  Stephenson  Link,  222.  Gooch  Link,  Allen  Valve, 
Double-ported  Slide-valve,  224.  Gridiron  Valve,  Valves  of  Auto- 
matic Cut-off  Engines,  Meyer  Valve,  225.  Buckeye  Valve,  Ideal 
Engine  Valve,  Valves  for  Slow-speed  Automatic  Cut-off  Engines, 
Corliss  Valves,  226.  Valves  taking  Steam  Internally,  227.  Re- 
leasing Gear  of  Corliss  Valve,  228.  Dash-pot,  Valves  of  Greene 
Engine,  229.  High-speed  Engine-governors,  230. 

CHAPTER  XXI. 

VALVE  DIAGRAMS 232 

Use  of,  Zeuner  Diagram,  232.  Explanation  of  the  Zeuner  Dia- 
gram, 233.  Geometric  properties  of,  234.  Examples  of,  236,  run- 
ning over  and  under,  direct  valve,  indirect  valve,  237.  Form  of 
diagram  for  different  conditions,  238.  Problems,  239. 

CHAPTER  XXII. 

ROTARY  ENGINES  AND  STEAM-TURBINES 241 

Piston  and  Abutment  of  Rotary  Engines,  Classes  of  Rotary 
Engines,  241.  Gearing  of,  242.  Packing  for  Piston  and  Abut- 
ment, Clearance  Space,  Advantages  of  Rotary  Engine,  243.  Ob- 
jections to,  244.  Steam-turbines,  244.  Hero's  Engine,  Branca's 
Engine,  Speed  of  Turbines,  Efficiency,  245.  De  Laval  Steam-tur- 
bine, 246.  Parsons  Steam-turbine,  248.  Curtis  Steam-turbine,  250. 
Kerr  Steam-turbine,  252. 

APPENDIX  TO  PART  II. 

APPENDAGES  TO  ENGINES 254 

Lubricator,  254.     Separator,  Steam,  255.     Oil-ceparator,  256. 


CONTENTS.  xiii 


PART   HI.     PUMP,    GAS-ENGINE,    WATER-POWER, 
COMPRESSED    AIR,    ETC. 

CHAPTER  XXIII. 

PAGE 

PUMPING  MACHINERY 257 

Suctions  and  Force-pumps,  257.  Air-chamber,  259.  Double- 
acting  Pump,  Classification,  260.  Steam,  Duplex,  Power,  Electric, 
Gas-engine,  and  Hydraulic  Pumps,  261.  Plunger  and  Piston, 
262.  Low-pressure  Pump,  High-pressure  Pump,  263.  Accumu- 
lator, 266.  Accumulator  and  Pump,  Pumps  for  Deep  Wells,  269. 
Air-lift,  Speed  of  Pumps,  Area  of  Water-valves,  271.  Water- 
piston,  Cylinders,  Government,  Mason  Governor,  272.  Measur- 
ing Water-pressures,  Capacity,  273.  Meter,  274.  Duty,  276. 
High-duty  Pumping  Engine,  Indicator-cards  from  Pump,  277. 
Problems,  278. 

CHAPTER  XXIV. 

GAS-ENGINES 280 

The  Gas-engine  Complete  as  a  Power  Producer,  Pressures  and 
Temperatures  of  Exploding  Gas,  280.  Classification,  281.  Four- 
cycle and  Two-cycle  Types,  Compression  of  Gas  necessary,  Otto 
Engine,  282.  Heavy  Construction,  Day  Engine,  284.  Manner  of 
averting  the  noise  of  the  Exhaust,  Indicator-cards  from  Gas- 
engine,  286.  Losses  in  a  Gas-engine,  Working  Fluid,  287.  Gas- 
producer  Plant,  Valves  and  Valve  Mechanisms,  288.  Regulation, 
Varying  the  number  of  Impulses  and  varying  the  strength  of  the 
Impulse,  289.  Centrifugal  and  Inertia  Governors,  290.  Igniters, 
291.  Gasoline-engines,  Difference  between  Gas-  and  Gasoline- 
engines,  Arrangement  of  Engine  and  Gasoline  Tank,  292.  Oil- 
engines, Atomizing  and  Vaporizing  of  the  Oil,  294.  Economy 
of  Oil-engine,  295.  Jacket-water,  296. 


CHAPTER  XXV. 

WATER-POWER 297 

Water-motors,  297.  Head,  297.  Velocity  Head,  etc.,  299.  Clas- 
sification of  Water-motors,  298.  Water-wheels,  299.  H.P.  of 
stream,  299.  Water-turbines,  300.  Efficiency  of  Water-turbines, 
303.  Runner,  303.  Manner  of  applying  Water  to  wheels,  303. 
Rating  of  Turbines,  306.  Speed  of  Turbines,  307.  Regulation, 
307.  Setting,  307.  Draft-tubes,  309.  Impulse  or  Jet  Wheels, 
309.  Pelton  Water-wheel,  309.  Hydraulic  Pump,  311.  Loss  of 
Head,  312.  Flow  of  Water  from  Orifice,  314.  Measuring  the 


xiv  CONTENTS. 

PAGE 

Power  of  Streams,  Velocity  of  Streams,  315.    Weir-dam  Measure- 
ment, 316.    Problems,  317. 

CHAPTER  XXVI. 

COMPRESSED  AIR 319 

Use  of  Compressed  Air,  319.  Manner  of  Compressing  Air,  Air- 
compressor,  320.  Details  of  Compression,  324.  Intercooler,  Fly- 
chest,  Temperature  due  to  Compression,  324.  Intercooler,  Fly- 
wheel, 325.  Air-receiver,  326.  Regulation,  Air-motors,  327. 
Rock-drill,  Air-brake,  328.  Laws  of  Air-pressure,  Relations  of 
Volume,  Pressure,  and  Temperature  of  Air,  329.  Diagram  of  Air- 
pressures,  Temperatures,  etc.,  329.  Volume  and  Weight  of 
Air  per  Minute,  333.  Indicators  and  Indicator-cards  from  Com- 
pressors, 334.  Horse-power  of  Compressors,  Freezing  of  the 
Exhaust  in  Motors,  336.  Friction  of  Air  in  Pipes,  336.  Problems, 
337- 

CHAPTER  XXVII. 

HOT-AIR  ENGINES 339 

Principle  of  the  Hot-air  Engine,   Ericsson   Hot-air  Engine,  339. 
Operation  of,  341.     H.P.,  Indicator-card,  342.     Problems,  343. 

TABLES. 

Table   I.  Properties  of  Steam 344 

"       II.  Weirs 347 

"     III.  Flow  of  Compressed  Air  through  Pipes 348 

"    IV.  Velocity  of  Water 349 


PART  I. 
MACHINERY  AND   MECHANICS. 


CHAPTER   I. 
INTRODUCTION. 

Engineering  is  the  art  of  constructing  and  using  machinery; 
or  the  art  of  executing  civil  or  military  works  which  require 
a  special  knowledge  of  machinery  or  of  the  principles  of 
mechanics. 

Mechanical  Engineering  is  that  branch  of  engineering 
which  has  to  do  with  machinery  such  as  machine-tools, 
engines,  etc. 

Civil  Engineering  is  that  branch  of  engineering  which 
relates  to  the  making  and  care  of  roads,  bridges,  railroads, 
harbors,  etc. 

Engineer. — This  is  the  term  applied  to  the  person  who  is 
skilled  in  the  principles  and  practice  of  any  branch  of  engineer- 
ing. Engineers  may  be  classed  according  to  their  occupa- 
tions, as  Mechanical,  Civil,  Military,  Naval,  Electrical,  Mining 
Engineers,  etc. 

Machinist. — This  name  is  given  to  one  who  is  familiar 
with  and  is  able  to  operate  machine-tools. 

Before  a  piece  of  machinery  can  be  in  readiness  for  use  it 
must  be  worked  upon  by  the  designer,  the  draughtsman,  the 
pattern-maker,  the  moulder,  and  finally  the  machinist.  The 
engineer  should  understand  the  principles  involved  in  the  work 


2  MACHINERY  AND  MECHANICS. 

of  each  of  the  above  men  and  should  have  had  enough  practice 
in  them  to  make  himself  reasonably  familiar  with  them. 

Mechanics  is  that  science  which  treats  of  the  action  of 
forces  on  bodies. 

A  Force  is  anything  that  tends  to  produce  or  change  motion 
in  a  body.  A  body  at  rest  is  put  in  motion  by  a  force ;  a 
body  in  motion  is  stopped  or  retarded  or  accelerated  by  a 
force.  Or,  if  the  direction  of  motion  of  a  body  be  changed, 
that  change  is  produced  by  a  force. 

The  unit  of  force  used  by  engineers  in  English-speaking 
countries  is  the  pound  avoirdupois.  For  some  scientific  pur- 
poses physicists  have  adopted  a  so-called  ' '  absolute  unit. ' ' 
This  unit  is  that  force  which,  acting  on  a  unit  mass  during  a 
unit  of  time,  will  produce  a  unit  of  velocity.  In  the  English 
system  it  is  the  force  which,  acting  for  one  second  on  a  mass 
whose  weight  is  one  pound  at  London,  will  produce  a  velocity 
of  one  foot  per  second.  It  is  equal  to  JL_  Ibs.,  or  roughly  half 
an  ounce.  As  a  unit  offeree  it  is  useless  to  engineers. 

A  Machine  is  a  combination  of  fixed  and  movable  parts 
so  disposed  and  connected  as  to  transmit  force  and  motion, 
in  order  to  secure  some  useful  result.  The  fixed  parts  con- 
stitute the  frame  or  support  for  the  moving  parts.  The  moving 
parts  constitute  a  train  or  trains  of  mechanism.  All  moving 
parts  of  machines  may  be  classified  as  follows : 

1.  Revolving  shafts.     Examples:  Line-shafts,  spindles,  etc. 

2.  Revolving    wheels    or    cams,    with    or    without    teeth. 
Examples:  Spur-gears,  pulleys,  etc. 

3.  Rods  or  bars  with  reciprocating  or  vibratory  motions  or 
both.      Examples:  The  piston-rod  of  an  engine;  the  connect- 
ing-rod of  an  engine;   links  of  all  kinds. 

4.  Flexible  connectors  depending  on  friction.      Examples: 
Belts,  ropes,  etc. 

5.  Flexible  connectors  not  depending-  on  friction.      Exam- 
ple: Link-belt. 

6.  A  column  of  fluid  in  a  pipe.      Examples:  Steam,  com- 
pressed air. 


INTRODUCTION.  3 

Simple  Machines. — The  simple  machines*  are:  (i)  the 
Lever,  (2)  the  Cord,  and  (3)  the  Inclined  Plane.  The  first 
includes  every  body  that  may  be  revolved  on  an  axis ;  the 
second  includes  all  machines  in  which  force  is  transmitted  by 
means  of  flexible  connectors ;  the  third  includes  all  machines 
in  which  a  surface  inclined  to  the  direction  of  motion  is  intro- 
duced. 

A  lever  is  a  rigid  bar,  movable  about  a  fixed  point  called  a 
fulcrum.  The  bar  may  be  straight,  bent,  or  curved.  Levers 
are  divided  into  three  classes,  according  to  the  relative  posi- 
tion of  the  applied  force,  the  weight,  and  the  fulcrum. 

In  a  lever  of  the  first  class  the  fulcrum  F  is  between  the 
applied  force  P  and  the  weight  W,  as  in  Fig.  I. 


1       t 

P 

FIG.  i. — Lever  of  the  First  Class. 


In  a  lever  of  the  second  class  the  weight  is  between  the 
applied  force  and  the  fulcrum,  as  in  Fig.  2. 


I 

w 

FIG.  2. — Lever  of  the  Second  Class. 


In  a  lever  of  the  third  class,  the  applied  force  is  between 
the  weight  and  the  fulcrum,  as  in  Fig.  3. 

The  law  of  the  lever  is  the  same  in  all  three  cases,  viz.: 
The  applied  force  multiplied  by  its  distance  from  the  fulcrum 


*  These  simple  machines  are  also  called  by  earlier  writers  on  Me- 
chanics the  "Mechanical  Powers."  This  term  is  now  becoming  obsolete. 
The  use  of  the  word  "  power  "  is  not  in  accordance  with  modern  usage,  in 
which  power  is  given  the  meaning  "  rate  of  doing  work," 


4  MACHINERY  AND  MECHANICS. 

is   equal   to   the   weight   multiplied   by  its    distance  from   the 
fulcrum. 

p 

't 


W 
FIG.  3.— Lever  of  the  Third  Class. 

If  the  direction  of  the  applied  force  or  of  the  resistance  is 
not  perpendicular  to  the  line  of  the  lever,  the  "  lever-arm  "  is 
the  perpendicular  distance  from  the  fulcrum  to  the  line  of  action 
of  the  applied  force  or  of  the  load. 

If  the  applied  force  P,  acting  through  a  distance  D,  moves 
the  load  W  through  a  distance  d,  then  PD  —  Wd.  This 
equation  may  be  stated  as  a  law,*  applicable  to  all  machines, 
viz.  :  The  weight  multiplied  by  the  distance  through  which  it  is 
moved  is  eqtial  to  the  applied  force  multiplied  by  the  distance 
through  which  it  acts. 

The  weight  of  the  lever  itself  is  sometimes  neglected,  but 
it  may  be  considered  as  an  additional  force  acting  at  the  centre 
of  gravity  of  the  lever. 

An  Inclined  Plane  is  usually  supposed  in  calculations  of 
machines  to  be  a  perfectly  hard  and  smooth  surface.  In  some 
cases,  however,  friction  is  taken  into  account.  The  weight  of 
a  body  on  an  inclined  plane  is  partly  supported  by  the  reaction 
of  the  plane.  But  as  this  reaction  is  normal  or  perpendicular 
to  the  plane,  a  body  on  it  will  slide  down,  unless  restrained 


FIG.  4. — Inclined  Plane. 

by  some  externally  applied  force.  If  this  force  be  applied  in 
a  direction  parallel  to  the  plane,  the  force  P,  Fig.  4,  will  be 
to  the  weight  as  the  height  of  the  plane  is  to  the  length  of  the 

*  Known  as  the  "  Law  of  Machines." 


INTRODUCTION.  5 

plane  measured  on  the  incline.      Expressed  as   an  equation, 

AB* 


P  = 


AC 


If  the  force  is  applied  in  a  direction  parallel  to  the  base  of 
the  plane,  then  will  the  applied  force  be  to  the  weight  as  the 
height  is  to  the  base;  or 


W  x  AB 


P  — 


These  equations  are  in  accordance  with  the  general  law 
stated  above.  For  if  the  weight  was  moved  the  entire  height 
of  the  plane  the  weight  would  be  moved  through  the  height 
AB.  To  move  the. weight  through  this  height  the  force  would 
be  required  to  act  through  the  whole  distance  AC  or  BC, 
according  to  the  direction  in  which  the  force  is  applied. 

If  the  force  be  applied  to  the  weight  in  any  other  direction 
than  the  two  just  stated,  the  relation  of  the  force  to  the  weight 
will  be  as  follows:  Let  a  (Fig.  5)  be  the  angle  the  plane 


FIG.  5. — Inclined  Plane. 

makes  with  the  horizontal,  and  6  the  angle  the  applied  force 
makes  with  the  surface  of  the  plane.  Then  the  force  will  be 
to  the  weight  as  the  sine  of  a  is  to  the  cosine  of  6\  or 


P  = 


W  X  sin  a 


cos 


*  The  equations  on  this  page  apply  only  to  a  body  in  equilibrium. 


MACHINERY  AND  MECHANICS. 


To  solve  problems  of  the  inclined  plane,  use  may  be  made 
of  the  triangle  offerees.      Thus  in  Fig.  6,  let  ^represent  the 


FIG.  6. — Inclined  Plane. 

weight  of  the  body  at  rest  on  the  inclined  plane,  c  being  the 
centre  of  gravity  of  the  body.  From  c  draw  a  line  ce  perpen- 
dicular to  the  surface  of  the  plane.  From  d  draw  a  line  ed 
parallel  to  the  surface  AC,  until  it  intersects  ec  in  e.  Then  in 
the  triangle  ced  the  force  due  to  gravity,  acting  on  the  body,  is 
represented  by  cd,  the  reaction  of  the  plane  by  ec,  and  the 
force  which  holds  the  body  at  rest  on  the  plane,  by  de.  If  no 
external  force  is  being  applied  to  hold  the  body  at  rest,  de 
represents  the  friction  force  acting  between  the  plane  and  body. 
Since  the  triangle  ABC,  representing  the  plane,  is  similar  to 
the  triangle  of  forces  ced,  the  sides  of  the  plane  may  be  used 
to  determine  the  relative  magnitude  of  the  forces  acting  on  the 
body.  Thus 

P:  W\\  ed\  cd::  AB  :  AC. 

A  Wedge  is  formed  by  two  inclined  planes  united  at  their 
bases.  Force  is  applied  to  a  wedge  at  its  head,  the  end 
directly  opposite  the  point.  The  work  of  a  wedge  and  of  an 
inclined  plane  differ  in  that  an  inclined  plane  is  generally  used 
to  assist  in  raising  a  weight,  while  a  wedge  is  generally  used 
to  penetrate  a  resisting  body.  Example:  The  use  of  a  wedge 
to  split  a  block  of  wood.  If  friction  be  neglected,  the  force 
required  to  penetrate  a  resisting  body  will  be  to  the  resistance 
as  the  thickness  of  the  wedge  is  to  the  length  of  the  wedge. 


INTRODUCTION.  1 

Thus,  letting  t  =  thickness,  /=  length,  P  the  force  applied, 
and  R  the  resistance,  P  \  R  ::/:/, 

P        Rt-       R-Pl 

e     ~         K  =  '- 


A  Screw  is  formed  by  wrapping  an  inclined  plane  around 
a  cylinder,  so  that  the  height  of  the  plane  is  parallel  to  the 
axis  of  the  cylinder.  A  nut  is  formed  by  wrapping  an  inclined 
plane  on  the  internal  surface  of  a  hollow  cylinder.  If  it  is 
desired  to  raise  a  weight  by  means  of  a  screw  and  nut,  force 
is  usually  applied  to  the  end  of  a  wrench  attached  to  the  screw, 
or  to  the  circumference  of  a  wheel  whose  axis  is  that  of  the 
screw.  Either  the  screw  or  nut  may  remain  fixed,  the  other 
being  rotated  in  order  to  raise  the  weight. 

If  r  be  taken  as  the  lever-arm,  or  as  the  radius  of  the  wheel 
to  which  the  force  P  is  applied,  /  the  pitch,  or  distance  between 
threads,  or  height  of  the  inclined  plane  for  one  revolution  of 
the  screw,  and  Wthe  weight  to  be  raised,  and  neglecting  fric- 
tion, P  :  W  \\  p  :  2nr\ 


6.2832;-' 


-_ 


In  practical  work,  however,  friction  cannot  be  neglected, 
as  a  large  part  of  the  applied  force  is  used  up  by  it,  making 
the  screw  a  very  inefficient  machine.  The  practical  applica- 
tions of  the  screw  will  be  treated  more  fully  in  Chapter  IX. 

The  Cam  is  a  revolving  inclined  plane,  which  may  be 
wrapped  around  a  cylinder  ;  or  it  may  be  curved  edgewise  and 
made  to  rotate  in  a  plane  parallel  to  the  base.  Its  mathe- 
matical treatment  is  the  same  as  that  of  the  screw.  The 
various  forms  of  cams  as  well  as  some  of  their  applications  will 
be  discussed  in  Chapter  X. 

The  Pulley  or  Block  consists  of  a  wheel  which  is  able  to 
rotate  freely  about  an  axis,  together  with  a  flexible  cord 
wrapped  around  a  portion  of  its  circumference.  The  axis  of 


MACHINERY  AND  MECHANICS. 


the  wheel  may  or  may  not  be  stationary;  hence,  pulleys  may 
be  classified  as  fixed  or  movable.  A  fixed  pulley  is  shown  in 
Fig.  7.  If  the  system  be  at  rest  the  tension  on  the  two  cords 
5  equal  and  the  applied  force  F  equals  the  weight  P. 


FIG.  7.  — Fixed   Pulley. 

A  movable  pulley  is  shown  in  Fig.  8.  Here  one  end  of 
the  cord  is  attached  to  a  fixed  support  at  A.  The  weight  W 
is  suspended  from  the  axis  C  of  the  pulley.  The  sum  of  the 
tensions  at  A  and  at  P  is  equal  to  the  tension  at  B,  due  to  the 
weight  W.  As  in  this  case  the  tension  at  A  is  equal  to  the 
tension  at  P,  P  =  %  W. 

Movable  and  fixed  pulleys  may  be  combined  as  shown  in 
Figs.  9  and  10. 

Fig.  9  shows  one  movable  and  one  fixed  pulley.  The 
fixed  pulley  revolving  about  C  merely  serves  to  change  the 
direction  of  the  force  P.  The  relation  of  P  to  W  is  the  same 
in  this  case  as  in  the  case  of  the  single  movable  pulley,  viz., 

/>=  \W- 

In  Fig.  10  there  are  three  fixed  and  three  movable  pulleys. 
The  weight  is  suspended  from  the  axis  B  of  the  movable 
pulleys.  Each  movable  pulley  has  two  plies  of  the  rope 


INTRODUCTION. 


engaging  it,  or  six  in  all.  These  six  plies  will  each  be 
shortened  by  the  amount  the  weight  is  lifted,  and  the  relation 
of  the  applied  force  to  the  weight  is  P  =  |  W.  In  general  the 
ratio  of  IV  to  P  is  equal  to  the  number  of  plies  that  engage  the 
lower  block,  and  also  to  the  number  of  plies  that  are  shortened 
by  the  raising  of  the  weight.  In  practice  the  pulleys  are 
seldom  arranged  as  shown  in  the  figure.  They  are  usually 
side  by  side  and  of  the  same  diameter.  If  the  upper  block  be 


FIG.  8. — Movable  Pulley. 


FIG.  9. 


FIG.  10. 


provided  with  three  sheaves  or  pulleys  and  the  lower  one  with 
two,  the  end  of  the  rope  will  be  fastened  to  a  hook  at  the  top 
of  the  lower  block.  In  this  case  five  plies  will  be  shortened 
instead  of  six  and  P  =  \W.  If  the  end  of  the  rope  to  which 
force  is  applied  pass  over  a  sheave  in  a  fixed  block,  the  force 
may  be  applied  in  any  direction  whatever.  If,  however,  the 
end  passes  over  a  sheave  in  the  movable  block,  then  will  it  be 
necessary  to  apply  force  in  a  direction  parallel  to  a  line  joining 
the  centres  of  the  pulleys.  If  the  force  be  applied  in  any  other 
direction,  the  pulley  will  be  drawn  out  of  the  line  joining  the 
weight  and  the  fixed  pulley,  and  the  maximum  effect  will  not 
be  obtained.  The  ratio  of  the  effective  pull  to  the  actual  pull 


«o  MACHINERY  AND  MECHANICS. 

will  be  equal  to  the  cosine  of  the  angle  made  by  the  rope  with 
the  vertical. 

The  Wheel  and  Axle  is  a  modification  of  the  lever.  The 
radius  of  the  wheel  may  be  regarded  as  one  arm  of  the  lever 
and  the  radius  of  the  axle  as  the  other.  Or  a  simple  arm  or 

wrench  may  be  fastened  to  the 
end  of  the  axle  instead  of  the 
wheel,  and  the  length  of  the  arm 
be  taken  as  the  length  of  one 
arm  of  the  lever.  Another  form 
of  the  wheel  and  axle  is  shown 
in  Fig.  ii.  Two  cylinders  or 
pulleys  of  different  diameters 
fastened  rigidly  together,  revolv- 
ing on  the  same  axis,  are  used 
to  raise  a  weight.  A  rope  is 
wound  around  the  larger  cylin- 
der, one  end  being  attached  to 
it.  The  weight  to  be  raised  is  attached  to  a  rope  fastened  to 
the  smaller  cylinder.  On  unwinding  the  rope  from  the  larger 
cylinder  A,  the  rope  attached  to  the  weight  will  be  wound  on 
the  smaller  cylinder  B.  If  D  represents  the  diameter  of  the 
larger  cylinder  plus  the  diameter  of  the  rope,  dihe  diameter  of 
the  smaller  cylinder  plus  the  diameter  of  the  rope,  P  the 
applied  force,  and  Wthe  weight, 


FIG.  ii. — Wheel  and  Axle. 


P  :  W\\  d\  D, 


p=Wd 
D   ' 


All  moving  parts  of  machines  can  be  resolved  into  these  simple 
"  Elements  of  Machines."  Applications  of  them  will  be  dis- 
cussed in  later  chapters. 


ENERGY,    WORK,    POWER,    ETC. 

A  Motor  is  any  producer  of  motion. 

Energy  is  the  ability  to  perform  work.      It  is  of  two  kinds, 
known  respectively  as  potential  and  kinetic  energy.      Potential 


INTRODUCTION.  .  n 

energy  is  the  ability  which  a  body  possesses  to  do  work,  owing 
to  its  position.  Thus  a  weight  raised  to  a  height,  or  water 
stored  in  a  reservoir,  both  possess  potential  energy.  Kinetic 
energy  is  the  energy  possessed  by  a  moving  body.  Thus  if 
the  raised  weight  be  allowed  to  fall,  or  the  stored  water  be 
allowed  to  flow,  both  the  weight  and  the  water  while  in  motion 
possess  kinetic  energy. 

Energy  manifests  itself  in  various  forms,  as  heat,  electricity, 
mechanical  energy,  chemical  energy,  etc. 

These  different  forms  of  energy  may  be  converted  one  to 
the  other.  Thus  heat  energy  is  converted  into  mechanical 
energy  in  the  steam-engine.  Chemical  energy  is  converted 
into  electric  energy  in  the  primary  battery,  and  mechanical 
energy  is  converted  into  electricity  in  the  dynamo. 

Conservation  of  Energy. — The  facts  stated  in  the  preced- 
ing paragraph  are  comprised  in  the  law  known  as  the  law  of 
Conservation  of  Energy.  This  law  states  that  "  No  form  of 
energy  can  ever  be  produced  except  by  the  expenditure  of 
some  other  form,  nor  annihilated  except  by  being  reproduced 
in  another  form.  Consequently  the  sum  total  of  energy  in  the 
universe,  like  the  sum  total  of  matter,  always  remains  the 
same."  (S.  Newcomb.) 

Potential  heat  energy  exists  in  coal  and  other  fuels. 
Potential  electric  energy  exists  in  a  charged  storage  battery. 
Potential  chemical  energy  exists  in  various  forms  as  in  gun- 
powder, etc.  The  measure  of  these  potential  energies  is  the 
amount  of  work  that  they  are  able  to  perform.  The  actual 
energy  of  a  moving  body  is  the  amount  of  work  it  will  do 
against  a  resistance  before  that  resistance  brings  it  to  rest. 
This  energy  is  equal  to  the  work  done  on  the  body  in  order 
to  bring  it  to  its  actual  velocity  from  a  state  of  rest. 

Kinetic  energy  is  mathematically  equal  to  \mi>*,  where  m, 

weight        weight 

the  mass  of  the  body,  — —  • ,  and  v  is  the  ve- 
locity at  the  instant  of  consideration.  It  is  also  equal  to  the 


12  MACHINERY  AND  MECHANICS. 

weight  of  the  body  multiplied  by  the  height  from  which  the 
body  must  fall  in  order  to  acquire  its  given  velocity.      Thus 

WV* 

E  =  Imv  =  wJi  =  -  —  . 


The  three  principal  sources  of  energy  on  the  earth  are  the 
muscular  energy  of  men  and  animals,  the  energy  of  wind  or  of 
flowing  water,  and  the  energy  of  fuels.  All  these  sources  of 
energy  are  due  to~the  heat  of  the  sun. 

The  first-named  group  is  the  least  important,  as  the  amount 
of  energy  available  in  either  men  or  animals  is  limited  by  the 
capacity  and  endurance  of  the  units.  Furthermore  there  is  no 
means  of  storing  energy  in  them.  The  second  group  is  more 
important  and  has  wider  application  than  the  first;  but  still  it 
is  not  absolutely  under  the  control  of  man.  Energy  may  be 
derived  from  flowing  water  only  in  certain  locations,  as  where 
there  is  a  waterfall  or  rapidly  flowing  stream.  Then,  too,  this 
energy  can  only  be  transported  to  limited  distances,  as  by 
means  of  electricity.  The  longest  transmission  line  for  a  heavy 
current  of  electricity  generated  by  a  waterfall  exists  at  present 
in  California.  The  line  is  about  150  miles  long.  The  energy 
due  to  winds  is  too  uncertain  to  be  depended  on  to  perform 
any  important  and  continuous  work. 

Thus  it  may  be  easily  seen  that  the  third  group  is  the  most 
important  source  of  energy.  Fuels  are  not  subject  to  the 
limitations  of  water,  wind,  and  man  power. 

An  enormous  capacity  for  doing  work  is  stored  up  in  very 
little  bulk;  it  maybe  liberated  from  the  fuel  as  gradually  as 
may  be  desired  and  the  quantity  is  not  limited.  It  may  be 
obtained  in  nearly  all  regions  and  if  not  found  in  certain  locali- 
ties it  may  be  transported  there.  The  most  -extensive 
application  of  this  mode  of  producing  energy  is  that  of  the 
Steam-engine  and  Boiler. 

Motive  power  has  different  characteristics  according  to  the 
nature  of  the  source.  It  may  be  constant  as  with  a  head  of 


INTRODUCTION.  13 

water  kept  at  a  certain  level  by  a  never-failing  stream,  or  it 
may  vary  according  to  fixed  laws,  like  the  action  of  steam  in 
an  engine-cylinder ;  it  may  be  irregular  as  that  of  the  muscular 
force  of  men  and  animals,  or  it  may  be  wholly  uncertain  as  in 
the  case  of  the  wind. 

These  characteristics  are  not  under  our  control,  so  that  we 
cannot  have  power  as  we  want  it  but  must  take  it  as  we  can 
get  it.  In  order  to  make  these  different  sources  of  power 
available,  some  arrangement  must  be  made  for  controlling 
them  and  making  them  serve  our  purposes.  This  is  done  by 
means  of  machinery. 

Work  is  the  overcoming  of  resistance  through  space.  The 
unit  of  work  is  the  foot-pound,  which  is  the  work  done  in  lifting 
one  pound  a  distance  of  one  foot.  Work  is  done  when  a  body 
is  raised  ii?  opposition  to  the  force  of  gravity.  This  is  the 
simplest  idea  of  what  is  meant  by  work.  In  general,  we  say 
that  work  is  done  in  moving  a  body  against  a  resistance  and 
the  resistance  is  overcome  by  the  action  of  force  upon  the  body 
moved.  From  this  it  is  seen  that  in  order  that  work  shall  be 
done,  motion  must  be  produced. 

Mathematically  speaking,  work  is  the  product  of  force  in 
pounds  multiplied  by  the  distance  through  which  the  force 
acts  in  feet,  and  this  product  is  generally  designated  as  so 
many  foot-pounds.  Thus,  if  10  pounds  be  lifted  through  a 
height  of  5  feet,  the  work  done  equals  10  X  5  —  50  foot- 
pounds. 

Efficiency. — In  any  machine  the  work  of  resistance  may 
be  divided  into  two  parts,  namely:  useful  work  and  lost  work. 
The  former  is  that  which  produces  desired  results  and  the 
latter  is  that  which  is  due  to  friction  and  other  causes.  Of 
course,  the  latter  is  much  smaller  than  the  former.  For 
instance,  in  the  arrangement  shown  in  Fig.  7,  a  force  of 
20  Ibs.  applied  at  F  in  the  direction  shown  by  the  arrow 
should  lift  an  equal  weight  of  20  Ibs.  applied  at  P.  But  owing 
to  the  friction  in  the  axle  of  the  pulley  and  in  the  cord,  a 
smaller  weight  will  be  lifted;  suppose  it  to  be  18  Ibs.  The 


14  MACHINERY  AND  MECHANICS. 

work  done  by  the  applied  force  in  moving  through  a  distance 
D  is,  in  this  case,  20  X  D  —  2oD. 

,  07} 

The  useful  work  is  1 8  X  D.      The  efficiency  then  is  — •=  = 

18 

—  =  90  per  cent. 

20 

We  are  now  prepared  to  define  efficiency.  Efficiency  is 
the  ratio  of  the  energy  utilized  by  a  machine  to  the  energy 
supplied  to  the  machine.  Or  it  may  be  expressed  as  a  frac- 
tion, viz.  : 

Work  obtained  from  machine 

Efficiency  =   ~^7 — =—    —v-—  —. L-. . 

Work  put  into  a  machine 

Power  is  the  rate  of  doing  work.  Thus  the  power  of  a 
machine  may  be  spoken  of  as  so  many  foot-pounds,  per 
second,  per  minute,  or  per  hour  as  the  case  may  be.  The  unit 
of  power  is  the  Horse-power,  which  is  equivalent  to  33,000 
foot-pounds  per  minute  or  550  foot-pounds  per  second.  An 
engine  of  one  horse-power  will  raise  one  pound  33,000  feet  in 
one  minute  or  33,000  pounds  one  foot  in  one  minute. 


PROBLEMS. 

1.  What  horse-power  will  be  required  to  lift  a  weight  of  40,000 
Ibs.  through  a  height  of  100  feet  in  one  minute? 

2.  What  horse-power  will  be  required  to  lift  a  weight  of  30,000 
Ibs.  through  a  height  of  1000  feet  in  ten  minutes  ? 

3.  A  pump  running  at  its  full  capacity  lifts  1000  gallons  of  water 
into  a  stand-pipe  50  feet  high  in  one  hour.      How  many  horse-power 
does  the  pump  produce,  exclusive  of  friction? 

4.  A  trip-hammer  weighing  2000  Ibs.,  operated  by  steam,  makes 
80  drops  per  minute,  the  drop  being  one  foot.       What  is  the  horse- 
power of  the  engine  that  runs  it,  supposing  that  the  efficiency  is  100 
per  cent  ? 

5.  An  elevator  rises   200  feet  to  the  top  of  a  building  in  four 
minutes.       What   horse-power  is  required  of  an    electric    motor   in 


INTRODUCTION.  15 

raising  it,  if  the  elevator  weighs  1000  Ibs.,  supposing  the  efficiency  to 
be  80  per  cent  ? 

6.  What  is  the  efficiency  of  an  1 8 -horse-power  engine  which  will 
lift  a  weight  of  10,000  Ibs.  through  a  height  of  loo  feel  iff  7  minutes, 
when  running  at  its  full  capacity? 


CHAPTER    II. 
SHAFTING. 

SHAFTING  is  employed  in  shops  for  transmitting  rotary 
motion  from  the  motors  to  the  operative  machinery. 

A  line-shaft  is  a  continuous  run  of  shafting  made  up  of  a 
number  of  lengths  joined  together  by  couplings,  and  may  or 
may  not  be  a  main  line-shaft. 

The  main  line-shaft  is  the  line  of  shafting  to  which  the 
engine  or  motor  is  attached,  and  which  imparts  motion  to  all 
the  other  shafts  and  machines. 

Counter-shafts  are  separate  sections,  usually  short  ones, 
placed  between  the  main  shaft  and  a  machine,  used  to  increase 
or  diminish  belt-speed,  to  alter  the  direction  of  belt-motion,  to 
carry  a  loose  and  a  fast  pulley  (so  that  by  shifting  the  belt  to 
the  loose  pulley  it  may  cease  to  communicate  motion  to  the 
machine),  or  for  all  these  purposes  combined, 

A  spindle  is  a  very  small  shaft,  and  is  usually  found  on 
machines. 

Hollow  shafting  is  used  to  a  large  extent  where  large 
quantities  of  power  are  to  be  transmitted ;  an  example  of  which 
may  be  seen  in  the  propeller-shafts  of  large  steamships.  It 
has  been  found  that  hollow  shafting  is  stronger  than  solid 
shafting  for  equal  quantities  of  metal. 

Flexible  shafting  is  used  to  transmit  rotary  motion  to  any 
desired  distance  from  the  power  source  through  any  number 
of  curves,  thus  allowing  the  power  to  be  carried  to  the  work 
instead  of  the  work  to  the  power.  It  is  used  extensively  for 
portable  work.  An  example  of  its  use  may  be  seen  in  the 
drilling  of  holes  for  the  rivets  in  locomotive-boilers  where  the 

16 


SHAFTING.  17 

magnitude  of  the  work  prevents  taking  it  to  a  drill-press  of  the 
ordinary  type.  A  more  common  example  is  the  instrument 
used  by  dentists,  the  power  being  transmitted  from  the  foot  of 
the  operator  by  means  of  a  small  flexible  shaft.  The  con- 
struction of  this  kind  of  shaft  varies  with  different  makes,  but  it 


FIG.  12.— Flexible  Shaft. 

is  generally  made  of  a  series  of  steel  wires  wound  upon  each 
other,  the  alternate  layers  running  in  opposite  directions.  At 
the  ends  fittings  are  attached,  one  to  receive  the  tools  which 
are  to  be  operated  and  the  other  to  receive  the  power  to  be 
transmitted. 

Shafting  is  generally  made  of  wrought  iron  or  steel  and  is 
made  cylindrically  true,  either  by  special  rolling  processes,  as 


i8 


MACHINERY  AND  MECHANICS. 


in  what  is  known  as  cold-rolled  or  hot-rolled  shafting,  or  else 
it  is  turned  in  the  lathe.  Very  large  shafting,  as  in  the  case  of 
propeller-shafts,  is  now  commonly  made  up  of  an  ingot  forged 
to  approximate  shape  and  then  turned  in  the  lathe  to  a  true 
cylinder.  Commercial  sizes  of  solid  shafting  are  made  from  J 
inch  upwards.  The  sizes  are  usually  given  in  odd  sixteenths 
of  an  inch,  and  advance  by  eighths.  Thus  IT5¥,  IT\,  i-^ 
inches,  etc.  The  shafting  is  rolled  or  turned  accurately  to 
the  dimension  given,  and  then  the  pulley  or  bearing  is  bored 
to  a  nice  fit. 

The  stresses  to  which  a  line  of  shaftirg  is  subject  are,  first, 
the  torsional  s.rtss  due  to  the  twisting  ef,~o:t  of  the  Lelt  on  the 
circumference  of  the  pulley;  and,  second,  the  transverse  stress 
due  to  the  weight  of  the  shaft  and  pulleys  and  to  the  pull  of 
the  belt  tending  to  bend  the  shaft.  In  order  to  keep  a  shaft 
from  moving  out  of  its  place  in  the  direction  of  its  length,  it  is 
necessary  to  use  a  collar  or  to  turn  a  shoulder  on  the  shaft 
itself.  A  shoulder  is  usually  inconvenient  to  manufacture,  and 


FIG.  13. — Collars.     A,  collar  fastened  to  shaft  with  a  set-screw;  B,  collar 
fastened  to  shaft  by  shrinking. 

consequently  the  collar  is  generally  used  for  this  purpose. 
The  collar  is  made  of  wrought  iron  or  steel,  and  may  be 
fastened  to  the  shaft  either  by  shrinking  it  on,  or  by  means  of 
set-screws.  The  collar  is  placed  on  the  shaft  against  the 
bearing,  and  prevents  the  shaft  from  moving  in  the  direction 
of  its  length.  If  the  set-screw  is  used  to  fasten  the  collar  to 


SHAFTING.  19 

the  shaft,  the  head  of  the  screw  should  be  sunk  into  the  collar 
enough  to  keep  it  from  catching  on  belts  or  clothing. 

Shafting  which  operates  wood- working  machinery  must  be 
run  at  a  higher  speed  than  that  used  for  most  metal-working 
machinery,  and  taking  this  as  an  example  it  is  seen  that  the 
speed  of  shafting,  in  general,  depends  on  the  kind  of  machinery 
it  is  employed  to  drive.  The  speed  of  shafting  runs  about  as 
follows  in  practice:  For  machine-shops  120  to  200  revolutions 
per  minute;  for  wood-working  250  to  300  revolutions  per 
minute;  and  {or  cotton-mills  300  to  400  revolutions  per  minute. 

The  cost  of  a  plant  may  be  lessened  by  running  the  line- 
shaft  at  a  high  speed,  rather  than  by  using  large  pulleys  on  it 
to  increase  the  belt-velocity.  The  diameter  of  the  shaft  should 
be  made  as  small  as  considerations  of  durability  will  allow. 
Larger  shafts  not  only  increase  the  weight  of  the  shafting, 
bearings,  couplings,  etc.,  thus  increasing  the  first  cost,  but  also 
cause  a  greater  amount  of  friction. 

A  given  diameter  of  shaft  will  transmit  more  power  in  pro- 
portion as  its  speed  is  increased;  that  is,  a  shaft  capable  of 
transmitting  10  H.P.  when  making  100  revolutions  per  minute 
will  transmit  20  H.P.  when  making  200  revolutions  per  minute. 

In  very  large  factories  long  lines  of  shafting  are  often  used, 
sometimes  as  much  as  1000  feet  in  length.  In  such  cases  the 


FIG.    14. — Shaft  with  Different  Diameters. 

shaft  is  much  larger  where  it  receives  the  power  irom  the 
engine  than  it  is  farther  away,  the  size  of  the  shaft  gradually 
diminishing  as  the  distance  from  the  motor  becomes  greater. 
This  consideration  suggests  another  practical  rule  which  should 
be  followed  when  it  is  possible ;  namely,  that  in  arranging  a 
machine-plant,  those  machines  requiring  the  greatest  amount 
of  power  should  be  placed  as  near  as  possible  to  the  motor,  in 
order  that  the  diameter  and  the  weight  of  the  shafting,  and  the 
friction  be  reduced  as  much  as  possible.  For  the  above 
reason,  in  sawmills,  the  large  saws  absorbing  most  power 


20  MACHINERY  AND  MECHANICS. 

should  be  driven  as  directly  as  possible  by  the  motor,  TV  Vile  the 
spaces  farther  from  the  motor  should  be  used  for  setting  up  the 
lighter  frame-  and  circular  saws.  Economy  in  the  quantity  of 
shafting  may  thus  be  practised,  as  the  twisting  effort  to  be 
resisted  by  the  shaft  becomes  less  and  less  as  the  end  most 
distant  from  the  motor  is  approached,  until  it  becomes  almost 
zero  at  the  end. 

The  following  rule  adopted  by  William  Sellers  &  Co. 
determines  the  size  of  the  shaft  to  be  used  when  the  horse- 
power is  given. 

RULE. — Divide  the  horse-power  by  tJie  revolutions  per  min- 
ute ;  multiply  the  quotient  by  125  and  extract  the  cube  root 
of  the  product.  The  result  is  the  diameter  of  shaft  required; 


3/125  H.P. 
=  A/ 


that  is,  d  •=  \  /  -    — ~- 

According  to  Dr.  R.  H.  Thurston,  this  coefficient  (125) 
varies  with  the  class  of  work  done  by  the  shaft,  and  also  with 
the  character  of  the  shaft.  The  coefficient  here  given  is  for 
an  iron  head-shaft,  well  supported,  and  having  bearings  placed 
close  to  the  pulleys.  For  a  cold-rolled  shaft  the  formula 

would  read,  d  =  \  /  -  ~ . 

\  K 

If  the  shaft  under  consideration  should  be  a  line-shaft,  with 
hangers  well  spaced,  say  seven  or  eight  feet  apart,  the  formula 


would  read  for  iron,  d  —  \—^—^  ',  for  cold-rolled  shafting, 

A 


c  c  "FT  P 

d  =  v        —  D~  —  '•      ^  the   snafting   is   used    only  to    transmit 


power,    and    there    are  no    pulleys  on  it,    the    formula    reads 

3  /62.5  H.P.  r  s  /35   H.P.    . 

d  —  A  /  --  =_.    _  for  iron  ;   d  —  A  /  --^—  -  -  for  cold-rolled 
y  K  y  K 

shafting.  Here  it  is  noticeable  that  the  size  of  the  shaft 
decreases  as  the  number  of  revolutions  increases,  showing  that 
it  is  more  economical,  as  far  as  shafting  is  concerned,  to  carry 
high  speeds. 


SHAFTING. 


21 


Couplings. — A  line  of  shafting  is  usually  of  considerable 
length,  and  must  therefore  be  composed  of  several  pieces 
united,  because  the  difficulties  of  construction,  of  transporta- 
tion, and  of  setting  up  forbid  its  being  made  in  a  single  piece. 
The  ends  of  the  different  pieces  are  united  by  means  of  coup- 
lings. Couplings  for  fastening  together  the  ends  of  the  sepa- 
rate sections  of  shafting  are  of  two  kinds,  viz. :  those  which 
may  be  used  to  couple  or  uncouple  at  will  while  the  shaft  is 
revolving,  and  those  which  require  that  the  rotation  of  the  shaft 
should  cease  in  order  to  effect  a  couple  or  uncoupling.  The 
former  is  called  a  Clutch. 

Fig.  1 5  shows  a  ^<?jr-coupling,  in  which  the  holding  power 
is  due  to  a  key.  It  consists  of  a  box  bored  out  to  fit  the  ends 


,  e^^^ 

r  T\  

______^:ii<£%i^>^^ 

I 

r 

'     ! 

FIG.   15. — Box-coupling. 

of  the  two   shafts  which  are  to  be  connected.      It  is  best  to 
make  the  key  in  two  pieces,  as  shown  in  the  cut.     The  first 


FIG.  16. — Flange-coupling. 

half  is  driven  in  tight  with  a  drift  and  afterwards  the  other  part 
is  placed  in  position.      By  this  method  it  is  not  necessary  to 


22 


MACHINERY  AND  MECHANICS. 


cut  the  key  and  keyway  so  accurately  as  when  the  key  is  in 
one  piece. 

Fig.  1 6  shows  a  Cast-iron  Flange-coupling.     The  cast-iron 


FIG.   17. — Cresson  Coupling. 

flanges  are  keyed  to  the  ends  of  the  shafts,  and  are  then  bolted 
together. 


FIG.  18.— Friction-clutch. 

In  the  Cresson  compression-coupling,  as  shown  in  Fig.  17, 
the  two  arms  at  A  and  B  are  made  to  clamp  the  shaft  by 


SHIFTING.  23 

means  of  the  taper-screws,  and  the  holding  effect  made  still 
greater  by  use  of  the  key. 

An  example  of  the  Clutch  is  shown  in  Fig.  1 8.  It  is  called 
a  friction-clutch.  AB  is  a  solid  piece  of  iron  of  conical  shape, 
which  admits  of  lateral  motion  on  the  shaft  P  from  left  to  right 
by  means  of  a  sliding  key.  CD  is  a  corresponding  piece  into 
which  AB  may  fit  and  which  is  fastened  to  the  shaft  Q  by 
means  of  a  key.  As  soon  as  the  one  slides  into  contact  with 
the  other,  the  friction  becomes  sufficient  to  engage  the  two 
lines  of  shafting. 

PROBLEMS. 

1.  A   cubic  foot  of  wrought    iron   weighs   480    Ibs.      Find  the 
weight  of  a  wrought-iron  shaft    20  feet  in  length  and   2  inches  in 
diameter. 

2.  According  to  the  rule  adopted  by  William  Sellers  &  Co.,  what 
is  the  required  diameter  of  a  line-shaft  which  makes  200  revolutions 
per  minute  and  transmits  125  horse-power? 

3.  What  diameter  will  be  required  in  the  above  shaft  if  it  is  making 
600  revolutions  per  minute  ? 

4.  What  horse-power  will  a  line-shaft  transmit  which  has  a  diam- 
eter of  2  inches  and  makes  400  revolutions  per  minute  ? 

Finding  the  Work  actually  transmitted  by  a  Shaft. — 
The  power  transmitted  by  a  shaft  is  measured  by  means  of 


FIG.   19. — Prony  Brake. 

Dynamometers,    of  which  there  are  two  classes:    Absorption 
Dynamometers  and  Transmission  Dynamometers. 


•24  MACHINERY  AND  MECHANICS. 

A  simple  form  of  the  former  is  shown  in  the  Prony  brake, 
Fig.  19.  The  shaft  whose  power  is  to  be  measured  is  clamped 
by  a  and  b,  two  blocks  of  hard  wood.  At  c  the  block  a  presses 
down  upon  platform-scales,  which  scales  measure  the  pressure. 
The  load  which  the  shaft  may  be  made  to  carry  is  increased 
by  tightening  the  hand-screw  Ji. 

Let  W—  work  of  shaft  in  foot-pounds  per  minute. 
"     P  =  pressure  in  pounds  registered  by  the  scales  on 

the  lever-arm  of  length  in  feet,  L. 
"     V  =  velocity  in  feet  per  minute  of  the  point  c  if  it  were 

allowed  to  rotate  with  the  shaft. 
"    N=  revolutions  of  shaft  per  minute. 
Then 


(i) 
......     (2) 

Combining  (i)  and  (2),  W=  2nLNP. 

W  27i  LNP 

H.P.  =  -        -,      hence     H.P.  =  ---  . 
33,000'  33.000 

The  shaft  may  be  the  crank-shaft  of  a  steam-engine,  gas- 
engine,  water-motor,  or  any  other  shaft. 

Dynamometers  are  used  principally  in  testing  motors  of 
different  kinds,  as  will  be  shown. 

Another  form  of  Prony  brake  is  shown  in  Fig.  20.  A  rope 
is  wound  about  a  pulley  ;  at  one  end  of  this  rope  known 
weights  are  attached;  the  other  end  of  the  rope  is  fastened 
to  the  spring-balance  which  is  securely  attached  to  the  floor. 
The  length  L  in  the  formula  is  the  radius  of  the  pulley.  The 
factor  IV  is  taken  as  the  difference  between  the  known  weights 
and  the  weight  registered  on  the  spring-balance.  A  Prony 
brake  or  any  other  absorption  dynamometer  absorbs  all  the 
work  that  may  be  done  by  the  engine  or  shaft  on  which 
it  is  used. 


SHIFTING. 


A  transmission  dynamometer  measures  the  power  that  is 
being  transmitted  through  a  shaft,  without  absorbing  any  of  it. 
There  are  a  number  of  forms  of  transmission  dynamometers, 


FIG.  20. — Rope  Prony  Brake. 

but  they  are  but-very  little  used  at  present.  For  descriptions 
of  them  see  Flather's  book  on  "  Dynamometers  "  and  the 
Transactions  of  the  American  Society  of  Mechanical  Engineers. 


CHAPTER    III. 
BEARINGS. 

A  BEARING  is  a  support  in  which  a  shaft  revolves. 
Generally  speaking,  the  bearing  is  fixed  and  the  shaft  revolves 
within  it;  but  sometimes  the  shaft  is  rigid  and  the  bearing 
revolves  around  it;  or  the  bearing  and  shaft  both  may  be 
movable  as  in  the  case  of  the  connecting-rod  end  and  crank 
or  cross-head  pins  of  an  engine. 

On  account  of  the  great  length  of  line-shafts  they  must  be 
supported  by  a  greater  number  of  bearings  than  is  necessary 
for  ordinary  axles  and  shafts,  for  which,  as  a  rule,  two  bearings 
are  sufficient. 

There  are  three  classes  to  which  all  bearings  may  be 
assigned,  viz. :  The  Journal-bearing,  the  Pivot-bearing,  and 


FIG.  21. — Journal-bearing. 

the  Collar-  or  Thrust-bearing.  If  the  pressure  on  the  bearing 
is  perpendicular  to  the  axis  of  the  shaft,  we  have  the  Journal- 
bearing. 

If  the  pressure  on  the  bearing  is  parallel  to  the  axis  of  the 
shaft,  and  the  end  of  the  shaft  rests  on  the  bearing,  it  is  called 

26 


BEARINGS. 


27 


a  Pivot-bearing.  If  the  pressure  on  the  bearing  is  parallel  to 
the  axis  of  the  shaft  and  the  shaft  passes  through  the  bearing 
we  have  the  Collar-bearing. 

The  journal-bearings   for  a  line-shaft  each    support    their 
proportional  part  of  the  weight  of  the  shaft,  and  also  the  pres- 


FIG.  22.— Pivot-bearing. 


FIG.  23. — Collar-bearing. 


sure  caused  by  the  pull  of  the  different  belts  leading  off  to  the 
machines.  In  the  case  of  the  pivot-bearing  the  weight  of  the 
whole  shaft  is  supported  by  the  one  bearing,  the  shaft  being 
kept  in  its  upright  position  by  other  journal-bearings  whose 


FIG.  24. — Ball-bearing. 


axes    are    vertical.      The   journal-bearing    is    the    class    most 
generally  used  and  is  found  in  all  kinds  of  machinery. 

A  notable  example  of  the  use  of  pivot-bearings  is  found  in 
water-turbines. 


28  MACHINERY  AND   MECHANICS. 

The  collar-bearing  has  the  advantage  that  it  will  not 
gradually  wear  and  let  the  shaft  drop  down,  as  is  the  case  with 
the  pivot-bearing,  because  any  number  of  collars  may  be  used 
on  the  same  shaft,  thus  increasing  the  bearing  surface  and 
lessening  the  vertical  wear 


FIG.  25.— Ball-bearing. 

Another  advantage  is  that  by  allowing  the  shaft  to  pass  on 
through  the  bearing,  pulleys  may  be  placed  beneath  it  and 
machinery  connected ;  also  the  bearing,  in  this  manner,  may 
be  kept  out  of  the  water,  which  would  be  desirable  in  the  case 
of  a  water-turbine. 


BEARINGS. 


29 


The  "ball-bearing  "  is  a  contrivance  for  lessening  the  fric- 
tional  resistance  by  doing  away  with  sliding-  friction  and  sub- 
stituting rolling-  friction  therefor.  It  may  be  used  with  either 
of  the  three  classes  named  above. 

The  "  roller-bearing  "  is  used  for  purposes  similar  to  those 
for  which  the  ball-bearing  is  used,  with  the  difference  that  the 
roller-bearing  is  used  for  heavier  work,  as  the  bearing  for  a 
line-shaft.  A  machine  fitted  with  ball-  or  roller-bearings  will 
run  with  a  saving  of  from  25  to  75  per  cent  of  the  power 
required  with  ordinary  bearings,  depending  upon  the  nature  of 
the  machine.  The  best  form  of  bearing  for  any  particular  use 
is  that  which  has  the  necessary  strength  and  at  the  same  time 
makes  the  least  possible  friction. 

A  "  built-up  bearing  "  is  one  made  of  two  or  more  pieces, 
so  arranged  that  it  may  be  adjusted  after  it  is  worn  so  that  it 
will  fit  the  shaft.  It  is  not  used  much  except  for  large  shafts, 
and  generally  consists  of  four  pieces,  viz.:  the  bottom,  the 
top  or  cap,  and  the  two  side  pieces.  The  two  side  pieces 
are  so  constructed  and  arranged  that  they  may  be  pushed 
closer  to  the  shaft,  after  they  are  worn,  by  means  of  wedges 
as  shown  in  Fig.  26.  A  bearing  which  is  suspended  from  a 


FIG.   26. — Built-up  Bearing. 

beam  is  called  a  ' '  hanger. ' '  Likewise  a  ' '  bracket  "  is  a 
bearing  which  supports  a  shaft  along  a  wall.  The  bearing  is 
made  an  easy  sliding  fit  on  the  shaft  in  order  that  the  shaft 


3° 


MACHINERY  AND  MECHANICS. 


may  turn  in  it.  The  length  of  a  bearing  depends  upon  the 
pressure  and  speed  of  the  shaft  which  it  supports.  Suppose 
the  pressure  upon  a  certain  bearing,  caused  by  the  pull  on  the 
shaft,  to  be  50  Ibs.  per  square  inch  of  bearing  surface ;  then  it 
is  not  likely  to  heat  because  there  is  not  enough  friction.  If, 


FIG.  27. — Hanger  with  Roller-bearing. 

however,  the  pressure  is  increased  to  100  Ibs.  per  square  inch 
there  may  be  a  heating  of  the  bearing ;  in  which  case  the  bear- 
ing should  be  made  twice  as  long,  thus  doubling  the  bearing 
surface  -and  making  the  pressure  50  Ibs.  per  square  inch  again. 
Thus  it  will  be  seen  that  the  length  of  the  bearing  is 
increased  in  order  to  lessen  the  pressure  per  square  inch  of 


BEARINGS.  31 

bearing  surface  by  increasing  the  number  of  square  inches.  If 
there  are  10  square  inches  in  a  bearing  surface  and  the  total 
pressure  is  1000  Ibs.,  then  the  pressure  per  square  inch  is 

-  =  100  Ibs.     Suppose,  however,  that  the  bearing  is  made 

twice  as  long,  then  there  will  be  10  X  2  square  inches  of 
bearing  surface,  and  the  pressure  per  square  inch  will  be 

1000 

—  =  50. 
20 

By  the  area  of  a  bearing  is  meant  the  area  of  its  projection 
on  a  plane  perpendicular  to  the  direction  of  the  pressure.  It 
is  sometimes  called  the  projected  area  or  bearing  surface. 

For  a  journal  of  diameter  D  and  length  Z,  the  bearing 
surface  would  be  DL. 

For  a  pivot-bearing,  the  bearing  surface  would  be  the  area 
of  the  cross-section  of  the  shaft,  .7854!)*. 

For  a  collar-bearing  the  bearing  surface  would  be  the  area 
of  the  collar,  .^8s4(Di2-D2),  DI  being  the  diameter  of  the 
collar,  and  D  the  diameter  of  the  shaft. 

Let  R  be  the  total  load  on  a  journal-bearing  and  /  the 

pressure  per  square  inch  of  bearing  surface.  Then  /  =  -=^.\ 
that  is,  /  equals  the  total  load  divided  by  the  number  of  square 

r> 

inches.       Likewise    for    a    pivot-bearing  p  =  ~    — — .       The 

•7°  54^ 

allowable  pressure  per  square  inch  /  varies  with  different 
speeds,  becoming  less  with  increasing  speeds;  but  for  ordinary 
journal-bearings  is  not  more  than  200  Ibs. ;  for  railway-axles 
1 60  to  300  and  for  collar-bearings  50  to  70  Ibs. 

Methods  of  applying  Oil  to  Bearings. — In  order  that  a 
bearing  may  not  heat,  it  is  important  to  keep  it  well  lubri- 
cated. Generally  it  is  best  to  feed  the  oil  to  the  bearing  by 
the  use  of  some  arrangement  which  will  deliver  it  automatic- 
ally, and  at  regular  intervals. 

Fig.  28  shows  what  is  called  a  Sight-feed  oiler.  This  is 
an  arrangement  by  which  the  oil  is  fed  to  the  bearing  drop  by 


32  MACHINERY  AND  MECHANICS. 

drop,  and  is  made  adjustable  so  that  the  oil  may  be  fed  as  fast 
or  slow  as  may  be  desired.  By  this  means  a  thin  oil  may  be 
used  on  large  bearings  where  heavy  oil  or  grease  would  other- 
wise have  to  be  used,  it  being  so  arranged  that  the  oil  is  resup- 
plied  to  the  bearing  as  fast  as  it  is  forced  out  by  the  heavy 
pressure. 

Fig.  29  shows  what  is  called  the  Compression  grease-cup, 
which  is  used  to  feed  tallow  or  other  heavy  greases  to  bearings. 


FIG.  28. — Sight  feed  Oiler.          FIG.  29. — Compression  Grease-cup. 

The  tension  in  the  spring  keeps  the  grease  pressed  down  into 
the  hole  in  the  cap  of  the  bearing.  Nearly  all  bearings  have 
grooves  cut  in  them  to  serve  as  reservoirs  for  surplus  oil  which 
is  put  in,  and  which  would  run  out  if  the  groove  were  not  there. 

PROBLEMS. 

1.  What  is  the  bearing  surface  in  square  inches  of  a  journal-bear- 
ing the  length  of  which  is  6  inches  and  diameter  4  inches  ? 

2.  What  is  the  bearing  surface  of  a  pivot-bearing,  the  diameter  of 
the  shaft  being  6  inches? 

3.  What  is  the  bearing  surface  of  a  collar-bearing  having   four 
collars,  the  diameter  of  the  shaft  being  6  inches  and  the  diameter  of 
the  collars  being  12  inches? 

4.  What  is  the  pressure  per  square  inch   upon  the  bearing  surface 
of  a  journal,  the  total  load  being  2400  pounds,  the   diameter  of  the 
bearing  4  inches,  and  the  length  6  inches  ? 


BE/tRINGS.  33 

5.  What  load  may  be  carried  by  a  journal-bearing  2  inches  in  diam- 
eter and  8  inches  in  length,  allowing  a  pressure  /  per  square  inch  on 
the  bearing  of  200  pounds  ? 

6.  A  shaft  is  3  inches  in  diameter  and   as  it  runs  at  a  high  speed 
can  run  safely  with  a  load  of  400  pounds  per  square  inch.     What 
should  be  the  length  of  the  bearing  if  the  total  load  is  6000  pounds  ? 

7.  Suppose  that  the  tension  on  the  tight  side  of  a  belt  is  3200 
pounds  and  the  tension  on  the  slack  side  1600  pounds;   what  will  be 
the  total  transverse  force  exerted  upon  the  shaft  to  which  it  transmits 
motion  ? 


CHAPTER    IV, 
FRICTION   AND    LUBRICATION   OF    BEARINGS. 

Friction  is  a  force  which  acts  between  two  bodies  at  their 
surface  of  contact  so  as  to  resist  their  sliding  on  each  other, 
and  which  depends  on  the  force  with  which  they  are  pressed 
together  (Rankine).  Friction  is  of  three  kinds:  sliding  and 
rolling  friction,  which  act  with  solids,  and  fluid  friction,  which 
acts  with  liquids  and  gases. 

On  every  surface  there  exists  microscopic  irregularities, 
which  offer  a  resistance  to  the  passage  of  one  surface  over 
another.  A  lubricant  introduced  between  the  two  surfaces 
tends  to  fill  the  irregular  spaces,  and  causes  the  surfaces  to 
approach  more  nearly  to  being  perfectly  smooth.  The  nearer 
a  surface  approaches  to  being  smooth,  the  less  frictional  resist- 
ance will  it  offer  to  the  passage  of  a  body  over  it. 

The  Coefficient  of  Friction  of  a  body  is  the  ratio  of  the 
force  required  to  slide  the  body  along  a  horizontal  plane  sur- 


FIG.  30. 

face,  to  the  weight  of  the  body, 
the  letter/. 


It  is  usually  designated  by 


34 


FRICTION  AND  LUBRICATION  OF  BEARINGS.  35 

The  Angle  of  Repose  of  a  body  is  the  angle  of  inclina- 
tion to  the  horizontal  of  a  plane,  on  which  the  body  will  just 
overcome  its  tendency  to  slide.  The  angle  of  repose  is 
usually  denoted  by  the  Greek  letter  0.  The  coefficient  of 
friction  is  equal  to  the  tangent  of  the  angle  of  repose ;  that  is 
/=  tan  6'. 

Morin's  Laws  of  Friction. — In  1831  Gen.  Morin  started 
a  series  of  experiments  which  extended  over  about  three  years. 
His  results  were  embodied  in  the  following  laws: 

1.  The  friction  between  two  bodies  is  directly  proportional 
to  the  pressure ;  that  is,  the  coefficient  of  friction  is  constant 
for  all  pressures. 

2.  The  coefficient  and  amount  of  friction,  pressure  being 
the  same,  is  independent  of  the  areas  in  contact. 

3.  The  coefficient  of  friction  is  independent  of  velocity. 
For   about   fifty  years   these   laws  were   accepted  without 

question  by  engineers.  Since  about  1880,  however,  experi- 
ments by  Thurston,  Tower,  and  others  have  shown  that  they 
are  in  error ;  in  fact,  not  even  approximately  true.  The  later 
experimenters  have  found  that  with  ordinary  machinery, 
friction  is  not  directly  proportional  to  the  pressure,  is  not 
independent  of  velocity;  and  that  the  coefficients  deter- 
mined by  Morin  were  about  ten  times  too  high  for  modern 
machinery. 

Prof.  J.  E.  Denton,  in  defence  of  the  laws,  claims  that 
Morin  made  no  such  special  preparations  for  his  tests  as  are 
made  to-day;  that  he  did  not  have  his  running  surfaces  so 
thoroughly  lubricated  as  in  modern  tests,  by  running  the  bear- 
ing in  oil,  or  by  means  of  an  oil-pad.  He  states  that  the 
conditions  under  which  Morin  worked  were  about  the  same  as 
exist  in  a  journal  lubricated  with  an  ordinary  restricted-feed 
oil-cup.  He  also  states  that  there  is  an  additional  resistance 
in  bearings,  due  to  the  viscosity  of  the  oil;  hence,  Morin's  laws 
will  not  apply  to  very  light  pressures. 

General  Morin  himself  states  that  the  laws  did  not  pretend 
to  be  mathematically  exact,  but  only  close  approximations 


MACHINERY  AND  MECHANICS. 


to  the  truth.  It  is  probable  that  the  laws  may  be  safely 
used  for  work  in  connection  with  ordinary  journals,  not 
specially  well  lubricated,  and  running  under  moderately  heavy 
pressure. 

The  experiments  of  Prof.  Thurston  showed  that  the  coeffi- 
cient of  friction  varied  with  different  conditions,  such  as  the 
nature  of  the  surfaces,  the  quality  of  the  lubricant,  etc.  He 
has  determined  the  coefficients  for  a  number  of  different  lubri- 
cants, surfaces  of  contact,  velocities,  etc. 

The  following  table  of  Prof.  Thurston  gives  the  coefficients 
of  friction  for  different  oils,  under  varying  pressures,  at  a  con- 
stant velocity  of  720  feet  per  minute,  the  journal  being  of  cast 
iron  and  the  bearing  of  bronze : 


Pressures,  Ibs.  per  square  inch  

8 

16 

32 

48 

Oils. 

Coefficients  of  Friction. 

to  .144 

"  .131 

"   .122 
"   .222 

Sperm,  lard,  neat's-foot,  etc.  . 
Olive,  cottonseed,  rape,  etc.. 
Cod  and  menhaden  

•159 
.160 
2d8 

to  .250 

"  .283 
"  .278 
"  .261 

.138  to  .192 

.107  "  .245 
.124  "  .167 

.145  ••  .233 

.086  to  .141 

.101    "   .168 
.097    "  .102 

.086    "   .178 

.077 
.079 
.081 
.094 

Mineral  oils  

I  ^  J. 

The  oil  was  fed  intermittently  through  an  oil-hole  and  at  a 
temperature  of  70°  F. 

The  following  laws  are  derived  by  Mr.  John  Goodman, 
from  the  experiments  of  Thurston,  Tower,  and  others. 

1.  The  coefficient  of  friction,  with  the  surfaces  well  lubri- 
cated, is  from  one  sixth  to  one  tenth  that  for  dry  or  scantily 
lubricated  surfaces. 

2.  The  coefficient  of  friction  for   moderate  pressures  and 
speeds  varies  approximately  inversely  as  the  normal  pressure; 
the  frictional  resistance  varies  as  the  area  in  contact,  the  normal 
pressure  remaining  constant. 

3.  At  very  low  journal-speeds  the  coefficient  of  friction  is 
abnormally  high,  but  as  the  speed  increases  from  about  10  to 
100  feet  per  minute,  the  friction  diminishes,   and  again  rises 


FRICTION  AND  LUBRICATION  OF  BEARINGS. 


37 


when  that  speed  is  exceeded,  varying  approximately  as  the 
square  root  of  the  speed. 

4.  The  coefficient  of  friction  varies  approximately,  in- 
versely as  the  temperatitre  within  certain  limits  ;  viz. ,  just  before 
abrasion  takes  place. 

It  has  been  found  by  experiment  that  metals  of  the  same 
kind  running  upon  each  other  sometimes  cause  more  friction 
than  do  metals  of  different  kinds;  the  probable  reason  being 
that  there  is  a  difference  in  microscopic  surface  structure ;  the 
minute  friction  points  do  not  so  accurately  correspond  and 
engage  each  other.  This  is  not  always  true,  however.  A 
hard-steel  shaft,  running  in  a  hard-steel  bearing,  properly 
polished,  has  very  low  friction. 

The  two  following  tables,  the  first  by  Rankine,  the  second 
by  Morin,  give  the  comparative  value  of  different  bearing 
surfaces. 

FRICTION  OF  MOTION. 


No. 

Surfaces. 

6. 

/ 

I-f-/. 

j 

\Vood  on  wood    dry. 

14°  to  26^° 

oc    tO       <? 

2 

"        "        "        soaped.  .  .  . 

IlT  to  2° 

26^°  to  31° 

.2   tO    .04 

5  to    6 

5  to  25 

4 

I-U°  tO   14° 

O  I    tO      26 

417  tO  ^    8^ 

TT!° 

6 

ni°  to  14° 

.2  tO      25 

5  to  J. 

28° 

I  80 

8 

"         "       '  '     wet.... 

l8i-0 

0  T 

Leather  on  oak  

I  ^°  tO  IQs-° 

27  to    38 

o   7  to  2  86 

10 

ii 

12 
13 

*4 

15 
16 

"         "    metals,  drv.  .  . 
wet... 
"          "         "        greasy 
oily... 
Metals  on  metals,  dry  
"        "         "        wet.  .  .  . 
Smooth  surfaces,  occasion- 
ally greased  

29l° 
20° 

13° 
**° 

8£°  to  11° 
i6j° 

4°  to  4i° 

.56 
.36 

•  23 
.15 

.15  tO  .2 

•3 
07  to    08 

1.79 
2.78 
435 
6.67 
6.67  to  5 
3-33 

17 

Smooth    surfaces,  continu- 
ously greased  

-7° 

c  ^ 

20 

18 

Smooth   surfaces,   best   re- 
sults   

l|°  tO  2° 

Q7   tO     O^6 

19 

Bronze    on    lignum    vitae, 
constantly  wet     

•7° 

0*? 

MACHINERY  AND  MECHANICS. 


COEFFICIENTS  OF  FRICTION  OF  JOURNALS  (MORIN). 


Material. 

Unguent. 

Lubrication. 

Intermittent. 

Continuous. 

j 

1 

r 

i 

Oil,  lard,  tallow. 
Unctuous  and  wet. 
Oil,  lard,  tallow. 
Unctuous  and  wet. 
Oil,  lard. 

Oil,  lard,  tallow. 

Oil,  lard. 
Unctuous. 
Olive-oil. 
Lard. 

.0710.08 
.14 
.07  to.  08 

.16 

.03  to  . 

.03  to  . 

.09 

.03  to  . 

054 
054 

054 

Cast  iron  on  lignum  vitae  .  . 
Wrought  iron  on  cast  iron. 
"       "  bronze.  .  . 

Iron  on  lignum  vitse  

.0710.08 
.11 

.19 

.10 

.09 

Bronze  on  bronze 

Cast-iron  Bearings  are  found  to  work  very  smoothly  under 
light  duty  provided  the  lubrication  is  perfect  and  the  surfaces 
can  be  kept  practically  free  from  dust  and  grit.  The  reason 
for  this  is  that  cast  iron  forms  a  hard  surface-skin  when  rubbed 
under  light  pressure,  and  so  long  as  the  pressure  is  not  enough 
to  cut  into  this  skin,  it  will  make  a  very  bright  and  smooth 
wearing  surface.  Another  point  in  favor  of  the  cast-iron  bear- 
ing is  that  it  will  hold  oil  better  and  longer  than  steel,  brass, 
or  wrought  iron.  This  may  be  proven  by  trying  to  clean 
the  oil  from  bearings  made  of  these  metals,  when  it  will  be 
seen  that  it  is  almost  impossible  to  clean  the  cast-iron  bear- 
ings, while  it  is  comparatively  easy  to  clean  the  others. 

Good  examples  of  the  superiority  of  cast-iron  are  found  in 
the  use  of  piston-rings  and  slide-valves.  .  It  has  been  found 
that  cast-iron  piston-rings  work  better  in  a  cast-iron  cylinder 
than  those  of  any  other  metal.  Where  the  seat  of  a  slide-valve 
is  of  cast  iron,  a  cast-iron  valve  will  cause  less  wear,  either 
to  itself  or  the  seat,  than  one  of  wrought  iron,  steel,  or  brass. 

Babbitt  Metal. — This  is  the  name  generally  given  to  cer- 
tain soft  compounds  used  in  bearings.  It  is  an  alloy  made  of 
tin,  antimony,  and  copper,  mixed  in  different  proportions,  de- 
pending on  the  kind  of  bearing  surface  desired,  whether  hard 
or  soft. 

Babbitt  is  used  in  bearings,  because  such  a  bearing  is  less 


FRICTION  AND  LUBRICATION  OF  BEARINGS.  39 

liable  to  "  overheat"  than  a  bearing  of  brass  or  bronze.  A 
bearing  of  Babbitt  will  also  permit  of  abrasion  or  crushing  with- 
out excessive  increase  of  friction.  The  various  kinds  of  Babbitt 
have  about  the  same  friction.  If  the  wearing  surfaces  are  kept 
in  good  order,  the  friction  will  depend  not  so  much  on  the 
metal  as  on  the  lubricant. 

In  order  to  use  Babbitt  metal  the  body  of  the  bearing  must 
be  made  considerably  larger  than  the  shaft,  and  then  a  bearing 
which  fits  the  shaft  perfectly  is  made  by  pouring  the  melted 
Babbitt  around  the  shaft  while  it  is  in  the  proper  position  within 
the  iron  part  of  the  bearing. 

Qualities  of  Good  Lubricants. — Good  lubricants  should 
have  the  following  qualities :  I .  Sufficient  body  (viscosity)  to 
keep  the  surfaces  free  from  contact  under  the  greatest  pressure. 

2.  The  greatest  fluidity  consistent  with  the  foregoing  condition, 

3.  Power  to  resist  oxidation  or  the  action  of  the  atmosphere. 

4.  Freedom  from  corrosive  action  upon  the  metals  with  which 
they  come  in  contact. 

Thus  it  will  be  seen  that  several  conditions  must  be  con- 
sidered in  the  selection  of  the  proper  kind  of  lubricant  for  a 
bearing.  The  main  consideration  is  the  amount  of  pressure. 

For  a  great  pressure  a  heavy  viscous  oil,  and  for  light 
pressure  a  more  fluid  oil  should  be  used. 

Oil  which  is  suitable  for  heavy  shafting  is  not  suitable  for 
small  spindles  such  as  are  used  in  clocks,  watches,  etc. 

Also  light  sperm-oil  is  equally  unsuited  for  heavy  pressures 
like  that  in  a  car-journal.  For  very  heavy  bearings  such  as 
those  of  rolling-mills  for  rolling  iron  and  steel,  tallow  and 
other  solid  lubricants  are  used.  It  is  said  that  in  the  Waltham 
Watch  Company  nineteen  different  kinds  of  oil  are  used,  so 
varied  is  their  machinery. 

There  are  three  kinds  of  lubricating  oils,  viz.  :  mineral, 
vegetable,  and  anima/ oils]  and  besides  these,  combinations  of 
two  or  more  of  them.  Soap  is  a  constituent  of  railway-grease ; 
graphite  and  steatite,  or  soapstone,  are  sometimes  used  for 
heavy  machinery. 


40  MACHINERY  AND  MECHANICS. 

The  following  list  shows  the  best  purpose  to  which  the 
various  lubricants  may  be  applied: 

For  steam-cylinders :   Heavy  mineral  oils. 

For  ordinary  machinery:  Lard-oil,  tallow-oil,  and  heavy 
mineral  or  vegetable  oils. 

For  very  great  pressures  with  low  speed:  Graphite,  soap- 
stone,  etc. 

For  heavy  pressures  with  low  speed:  Tallow,  lard, 
grease,  etc. 

For  heavy  pressures  with  high  speed:  Sperm-oil,  castor- 
oil,  mineral  oils. 

For  light  pressures  with  high  speed:  Sperm,  refined  petro- 
leum, cottonseed,  rape,  and  olive  oils. 

For  watches,  clocks,  etc.  :  Light  mineral  oils,  clarified 
sperm,  neat's-foot,  olive,  and  porpoise. 

Sperm,  lard,  olive,  and  cottonseed  oils  may  be  mixed  with 
minerals  oils.  Sperm  makes  the  best  mixture.  The  value  of 
the  others  in  mixtures  is  in  the  order  given. 

It  should  be  stated  that  in  all  cases,  where  possible,  a 
mineral  oil  of  suitable  body  should  be  selected.  If  fatty 
vegetable  oils  are  used  in  connection  with  high  temperatures, 
such  as  exist  in  the  cylinder  of  a  steam-engine,  the  oil  will  be 
decomposed,  forming  fatty  acids,  which  in  the  presence  of  the 
metal  will  form  metallic  soaps,  and  may  cause  great  damage 
to  the  machinery. 

Graphite  is  a  solid  lubricant ;  it  is  most  used  in  the  form 
of  a  powder.  It  will  work  well  either  used  alone  or  in  con- 
nection with  various  oils.  It  is  principally  used  in  connection 
with  heavy  pressures,  but  Thurston  states  that  it  may  be  used 
to  advantage  either  for  light  or  heavy  pressures,  especially 
when  mixed  with  certain  oils.  It  is  rather  difficult  to  intro- 
duce into  bearings,  being  a  solid.  Mixing  it.with  water  or  oil 
will  facilitate  its  use,  however. 


CHAPTER    V. 
FRICTION-WHEELS. 

THE  use  of  friction-wheels  gives  the  simplest  method  of 
transmitting  motion  from  one  shaft  to  another  by  means  of 
wheels,  the  belt  or  chain  being  made  unnecessary  in  this  case. 
The  transmission  of  power  is  often  effected  by  pressing  the 
two  wheels  together  at  their  circumferences,  but  sometimes 
the  circumference  of  one  wheel  presses  on  the  disk  of  the  other. 
The  transmitting  power  is  due  to  the  friction  of  the  wheels 
upon  each  other.  The  materials  used  in  their  construction 
must  be  such  that  the  coefficients  of  friction  will  be  as  great  as 
possible,  so  that  the  pressure  between  the  two  wheels  will  not 
have  to  be  abnormally  great.  For  the  above  reasons  wood  is 
often  made  to  work  with  wood,  cr  wood  with  cast  iron. 
Sometimes  the  perimeters  of  the  wheels  are  covered  with 
leather.  Small  friction-wheels  are  sometimes  made  of  solid 
disks  of  leather,  and  sometimes  of  similar  disks  made  of  coarse 
paper  and  compressed  into  the  proper  form  and  stability  by  the 
use  of  hydraulic  pressure. 

In  other  cases  grooves  are  cut  in  the  circumference  of  the 
wheels.  The  projections  on  one  wheel  are  forced  into  the 
grooves  in  the  other.  In  this  manner  a  greater  bearing-surface 
is  obtained  than  ordinarily.  A  pair  of  such  wheels  is  shown 
in  Fig.  31. 

The  great  objection  to  the  use  of  friction-wheels  is  that  in 
order  to  produce  an  adequate  transmitting  friction  at  the  sur- 
face of  the  wheels  an  excessive  quantity  of  friction  and  wear  is 
produced  in  the  bearings.  Another  objection  to  the  use  of 
friction-wheels  is  that  the  bearings  of  the  two  wheels  cannot 

41 


MACHINERY  AND   MECHANICS. 


both  be  fixed,  because  it  is  by  moving  the  two  wheels  closer 
together  that  the  pressure  can  be  increased  between  the  two, 


FIG.  31. — Friction-wheels. 

and  this  can  only  be  done  by  moving  the  bearings  nearer  to 
each  other.  On  this  account  the  friction-wheels  are  used 
comparatively  little. 

It  is  thought  best,  however,  to  discuss  them  here  for  the 
reason  that  the  principles  of  mechanism  which  are  shown  in 


FIG.  32. 


their  discussion  are  applicable  also  to  other  circular  gearings, 
especially  to  toothed  gears.      In  Fig.  32  we  have  two  friction- 


FRICTION-WHEELS. 


43 


wheels  in  which  the  contact  is  between  the  axes,  and  in  Fig. 
33  two  friction-wheels  in  which  the  contact  is  outside  of  the 
axes,  the  axes  being  parallel  in  each  case.  Again  in  Fig.  34 


FIG.  34. 


FIG.  35- 

we  have  a  case  in  which  the  axes  meet,  the  contact  being 
in  the  acute  angle.  Fig.  35  shows  intersecting  axes  with  the 
contact  in  the  obtuse  angle. 


44  MACHINERY  AND  MECHANICS. 

The  ratio  of  the  rotative  speeds  to  the  radii  of  the  wheels 
in  any  of  the  above  cases  may  be  obtained  graphically,*  and 

A         : an  example  is  here  given  of  each. 

In    Fig.    36    let   R   represent    the 

radius  of  the  large  wheel   and    r 

_Jr ^Ssxv/    the  radius  of  the  small  wheel,    V 

/  the  velocity  of   the    large  wheel, 

FIG.  36.  and   v  the   velocity  of  the   small 

wheel.      The   velocities  of  the  two  wheels   geared   with  each 

V        r 
other  are  to  each  other  inversely  as  their  radii;   hence  —  =  -=-. 

v        A 

Suppose  it  is  desired  that  the  two  fixed  axes  A  and  B  be  con- 
nected by  wheels  of  such  radii  that  their  velocities,  or  number 
of  revolutions,  shall  be  to  each  other  as  2  to  5.  As  the  sum 
of  the  radii  equals  the  distance  between  the  axes,  by  addition, 
we  have  5  -f-  2  =  7.  Draw  any  line  AB,  seven  units  in 
length,  which  length  should  be  greater  than  the  distance 
between  the  axes.  Take  the  distance  AC  equal  -to  five  units 
and  CB  equal  to  two  units.  Through  C  draw  CD  parallel  to 
the  axes.  Perpendiculars  R  and  r  from  any  point  of  the  axes 
to  the  line  of  contact  CD  will  be  the  required  radii. 

Contact    outside    of  t/te    Axes. — In  this  case  the  distance 
between  the  two  axes  must  be  equal  to          A 
the  difference  R  —  r  of  the   two  radii. 
In  Fig.  37  take  A   and  B  again  for  the 
axes.      It  is  desired  to  find  the  point  C 


outside  the  axes  A  and  B.      Taking  the    D  c 

same    velocity   ratio,    2    to    5,   we    have  FIG.  37- 

5—2  =  3.  Draw  a  line  AB,  in  length  three  units,  the  differ- 
ence (R  —  r),  and  greater  than  the  distance  between  the  axes. 
Produce  this  line  to  C,  making  BC  equal  to  two  units. 
Through  C,  draw  CD  parallel  to  the  axes.  Perpendiculars 
from  CD  to  the  axes  will  be  the  required  radii. 

These  two  constructions  may  be  dispensed  with,  if  the  dis- 

*  The  constructions  given  on  pages  44  and  45   are  taken  from   Robin 
son's  "  Principles  of  Mechanism." 


FRICTION-WHEELS.  45 

tance  between  the  axes  is  divisible  into  a  convenient  dimension 
by  the  sum  or  difference  of  the  velocity  ratio  as  the  case  may 
be.  If  the  distance  is  so  divisible,  the  divisions  may  be  made 
on  the  perpendiculars  to  the  axes  themselves. 

Axes  Meeting — Contact  between  Axes. — In  Fig.  34  take 
A  O  and  BO,  intersecting  at  O  as  the  axes,  which  are  to  be 
connected  by  friction-wheels  so  that  their  velocities  of  rotation 
shall  be  as  2  to  5,  as  in  the  previous  examples.  Lay  off  on 
OA  from  0,  the  distance  Oa  =  2,  the  relative  velocity  of  A, 
and  on  OB  the  relative  velocity  of  B,  which  is  Ob  =  5. 

Complete  the  parallelogram  Oacb,  thus  finding  the  point  c. 
Through  O  and  c  draw  the  line  cO.  This  line  will  be  the  line 
of  contact  of  the  two  wheels.  Any  number  of  wheels,  varying 
in  size  but  with  the  same  velocity  ratio,  may  be  constructed 
upon  it  as  a  line  of  contact.  Thus  the  diameter  FBm  may  be 
drawn  and  its  mate  will  be  mRE,  r  and  R  being  the  radii. 

The  same  construction  may  be  applied  to  a  case  in  which 
the  axes  meet,  but  with  contact  outside  of  them.  The  con- 
struction is  shown  in  Fig.  35,  the  lettering  being  the  same  as 
for  the  preceding  case.  No  further  explanation  is  necessary. 

It  is  noticeable  that  friction  wheels,  as  well  as  all  other 
gear-wheels,  always  work  in  pairs.  The  one  which  imparts 
motion  is  called  the  Driver,  and  the  one  which  receives  motion 
is  called  the  Driven  wheel,  or  Follower.  As  has  already  been 
stated,  the  ratio  of  the  revolutions  of  two  friction-wheels  in 
gear  is  inversely  as  the  ratio  of  their  radii.  Let  A7  =  number 
of  revolutions  of  the  driver,  ;/  =  revolutions  of  driven,  R  = 
radius  of  driver,  and  r  =  radius  of  driven ;  then  the  equation, 
N  X  R  =  n  X  r,  shows  the  relation  of  velocity  and  radii. 

PROBLEMS. 

1.  Two  parallel  shafts  are   18    inches    between    centres.      Find 
graphically  the  radii  of  the  two  friction-wheels  such  that   one  shaft 
will  make  4  revolutions  to  5  of  the  other,  the  contact  coming  between 
the  axes. 

2.  Two   parallel    shafts    are    8    inches    between    centres.     Find 


46  MACHINERY  AND  MECHANICS. 

graphically  the  radii  of  two  friction-wheels  such  that  one  may  make  5 
revolutions  to  6  of  the  other,  the  contact  coming  outside  the  axes. 

3.  The  axes  of  two  shafts  meet  each  other  at  an  angle   of  45 
degrees.      Find  graphically  the  size  of  the  conical  friction-  wheels  such 
that  one  may  make  2  revolutions  to  3  of  the  other,  the  contact  being 
in  the  acute  angle. 

4.  In  Fig.  32  let  the   radius  of  the  wheel  A  =  12   inches  and  the 
radius  of  B  =  3  inches.      If  A  makes  100  revolutions  per  minute,  how 
many  revolutions  will  .Z?make  per  minute? 

5.  In  Fig.  33  let  the  radius  of  the  wheel  A  =  16  inches  and  the 
radius  of  B  —  2  inches.     If  B  makes  400  revolutions  per  minute,  how 
many  will  A  make  ? 

6.  In  Fig.  32  2?and  A  make  1200  and  200  revolutions  per  minute 
respectively,  and  A  is    18  inches  in  diameter.      What  must  be   the 
diameter  of  B  ? 

7.  In  Fig.  33  B  and  A  make    900  and   100  revolutions  per  min- 
ute respectively,  and  B  is  2  inches  in  diameter.     Find  the  diameter 


8.  The  axes  of  two  shafts  make  an  angle  of  120°  with  each  other. 
The  driver  is  to  make  two  revolutions  to  one  of  the  follower,  and  the 
contact  is  to  be  in  the  obtuse  angle.     Find,  graphically,  the  two  wheels. 

9.  Same  as  in  problem  8,  except  that  the  driver  is  to  make  three 
revolutions  to  one  of  the  follower. 


CHAPTER   VI. 
PULLEYS. 

PULLEYS  for  the  transmission  of  power  by  belts  are  divided 
into  two  classes:  the  solid  and  the  split  pulley.  The  solid 
pulley  may  be  cast  solid,  or  the  hub  and  arms  may  be  cast  and 
a  rim  of  wrought  iron  or  steel  riveted  on.  The  latter  makes 
a  strong  and  light  pulley. 

The  split  pulley  may  be  made  of  iron  or  wood.  In  either 
case  the  two  halves  are  bolted  together  tight  enough  to  clamp 
the  shaft.  When  the  wood  pulley  is  used  a  bushing,  made  of 
two  or  more  pieces  of  wood,  is  put  around  the  shaft  and  into 
the  eye  or  hub  of  the  pulley  in  order  to  make  a  tight  fit. 
Pulleys  are  sometimes  made  without  arms,  but  with  a  solid 
web  instead. 

Owing  to  the  fact  that  very  large  castings  sometimes  cool 
unequally,  and  consequently  cause  shrinkage,  rendering  break- 
age liable,  it  is  customary  to  cast  pulleys  of  larger  diameter 
than  6  feet  in  two  or  more  parts.  This  lessens  the  liability  to 
damage  by  shrinkage,  and  at  the  same  time  makes  the  pulley 
easier  to  handle. 

Pulleys  of  small  diameter,  that  is,  up  to  3  feet,  are  usually 
fastened  on  the  shaft  by  means  of  set-screws.  Pulleys  of 
larger  diameters  than  3  feet  are  usually  fastened  by  keys,  and 
sometimes  by  both  keys  and  set-screws.  In  either  of  these 
cases,  if  the  bore  in  the  hub  of  the  pulley  is  larger  than  the 
shaft,  which  is  generally  the  case,  in  order  that  the  pulley  may 
be  slipped  on  with  ease,  the  pulley  will  be  out  of  balance  when 
the  pressure  of  the  set-screw  is  placed  against  it. 

Especially  in  the  case  of  pulleys  running  at  high  speeds  it 

47 


4  MACHINERY  AND  MECHANICS. 

is  often  necessary  to  balance  the  rim  by  some  means,  in  order 
to  counteract  this  objectionable  feature.  This  may  be  done 
by  attaching  a  small  iron  weight  to  the  inner  side  of  the  rim 
opposite  the  heavy  side,  as  in  Fig.  38.  When  the  pulley  is 
unbalanced  it  causes  the  shaft  to  vibrate  when  rapidly  revolv- 


FIG.  38. — Split  Pulley. 

ing,  and  this  causes  unequal  strains  in  the  belt  at  different  parts 
of  the  revolution,  not  only  injuring  the  shaft  and  bearing,  but 
stretching  and  wearing  the  belt. 

A  pulley  which  transmits  motion  to  a  belt  is  called  a 
driver.  A  pulley  which  receives  motion  from  a  belt  is  called 
a  driven  pulley.  A  pulley  is  said  to  be  crewnfrfv/hen  the  face 
of  the  rim  is  curved,  the  largest  diameter  being  at  the  middle. 
This  is  done  in  order  that  the  belt  may  be  kept  from  running 
off,  because  the  belt  tends  to  run  where  it  is  kept  tightest. 
The  amount  of  convexity,  in  practice,  varies  from  -^  to  T36  inch 
per  foot  of  width  of  pulley-face. 

A  Fast  pidley  is  one  which  is  fastened  to  the  shaft  and 
transmits  motion  from  one  pulley  to  another  by  means  of  belts 
and  ropes. 

A  Loose  pulley  runs  free  on  the  shaft  in  order  to  receive  the 


PULLEYS. 


49 


belt,  and  at  the  same  time  transmit  no  motion  to  the  shaft  to 
which  it  is  attached.  It  is  generally  used  on  countershafts  for 
throwing  machines  in  or  out  of  gear,  and  has  no  convexity, 
or  crown,  on  the  face,  in  order  that  the  belt  may  be  moved 
aside  easily. 

A  Cone  or  Stepped  pulley  has  a  number  effaces  or  grooves 
of  different  diameters  whereby  the  speed  of  a  machine  may  be 
changed ;  examples  of  cone  pulleys  may  be  seen  on  wood-  or 


FIG.  39. — Cone  Pulley. 

engine-lathes.  These  cone  pulleys  always  work  in  pairs,  one 
on  the  machine  which  is  operated  by  the  belt  and  one  on  the 
countershaft.  A  method  of  designing  cone  pulleys  is  given  at 
the  end  of  this  chapter. 

Conical  pulleys  are  used  where  it  is  desired  that  a  uniform 
speed  be  changed  to  a  variable  speed,  or  for  changing  a 
variable  speed  to  a  uniform  speed.  They  work  in  pairs  like 
the  cone  or  stepped  pulleys.  An  example  may  be  found  in 
cotton-factories  where  it  is  necessary  to  give  the  bobbins  a 
gradually  increasing  speed  on  account  of  the  unwinding  of  the 
thread  from  the  bobbin. 

A  modification  of  belted  conical  pulleys  is  shown  in  Fig. 
40,  which  operates  upon  the  principle  of  friction-gearing. 
Motion  being  desired,  the  ring  of  leather  is  moved  endwise 
by  a  suitable  shifting  device,  and  by  reason  of  the  ring  filling 
up  the  space  between  the  pulleys,  motion  is  imparted  from 


MACHINERY  AND  MECHANICS. 


the    driving    pulley    to    the    driven     pulley,    and     so     to     the 
machinery. 

In  all  the  cases   described  above,   the  pulleys  have  been 
circular  in  perimeter,  but  non-circular  or  cam-shaped  pulleys 


FIG.  40. — Evans'  Friction  Cone  Pulley. 

are  used  occasionally  for  producing  special  movements  in 
which  it  is  required  that  the  velocity  of  the  driven  should  be 
variable  at  different  parts  of  the  revolution.  See  Fig.  41. 


DRIVER 


FIG.  41. — Variable  Velocity  Pulley. 

An  example  of  a  pulley  in  which  the  axis  of  the  pulley 

does  not  coincide  with  the  axis 
of  rotation  is  found  in  the  foot- 
power  lathe-treadle,  shown  in 
Fig.  42,  which  is  self-explana- 
tory. 

The  driving  power  of  a  belt 
and  pulley  is  increased  by  mak- 
ing the  face  of  the  pulley 
smoother.  The  holding  power 
of  a  belt  does  not  depend  upon 
FiG.42.-Lathe-treadle.  the  friction  between  the  belt 

and  the  pulley-face  but  upon  the  adhesive  force  between  the 


PULLEYS.  51 

two.  The  adhesion  depends  on  the  intimacy  of  contact,  and 
as  smoothness  of  the  two  surfaces  produces  a  contact  between 
a  larger  number  of  particles,  it  is  plain  that  the  above  state- 
ment is  true.  A  very  smooth  contact  also  produces  a  partial 
vacuum  between  the  belt  and  the  pulley  which  increases  the 
tractive  force  of  the  belt. 


FIG.  43.  —  Countershaft. 

If  there  is  no  slip  in  the  belt-connector,  the  revolutions  of 
two  connected  pulleys  will  vary  inversely  as  their  diameters, 
and  the  relation  of  velocities  to  the  diameters  of  the  driver  and 
driven  is  the  same  as  that  for  friction-wheels. 

Let  D  =  diameter  of  driver; 
d  =  diameter  cf  driven  ; 
N=  revolutions  of  driver; 
n  =  revolutions  of  driven. 

Then  the  following  equations  express  the  relations  of  the 
two  pulleys  with  regard  to  the  number  of  revolutions  and 
diameters  : 


D  ' 


n 

Where  a    system   of    pulleys    is    used,   the  following    rule 
shortens  the  calculation : 


52 


MACHINERY  AND  MECHANICS. 


RULE. —  The  revolutions  of  the  first  driver  multiplied  by  the 
continued  product  of  the  diameters  of  the  drivers  is  equal  to  the 
revolutions  of  tJie  last  driven  multiplied  by  the  continued  product 
of  the  diameters  of  the  driven  pulleys. 

Design  of  Cone  Pulleys. 

The  following  method  of  designing  cone  pulleys  is  taken 
from  Kent's  "Mechanical  Engineers'  Pocketbook. "  Let 
EF,  Fig.  44,  be  the  distance  between  the  centres  of  the 


FIG.  44. — Design  of  Cone  Pulleys. 

pulleys.  Draw  the  circles  Dl  and  d^  representing  the  first 
pair  of  pulleys.  The  diameters  of  this  first  pair  can  be  deter- 
mined by  given  conditions.  Draw  JK  tangent  to  the  circles 
Dl  and  dr  At  B,  the  middle  point  of  EF,  erect  a  perpendic- 
ular BG.  The  length  of  BG  should  be  .3  14  EF.  With  G  as 
a  centre  draw  a  tangent  circle  to  JK.  The  belt-line  of  any 
other  pair  of  pulleys  must  be  tangent  to  this  circle,  Take  any 
line  as  HI  or  LM.  The  circles  about  E  and  F  drawn  tangent 
to  it  will  be  one  of  the  required  pairs. 


PROBLEMS. 

1.  In  Fig.  43  A  makes  TOO  revolutions  per  minute,  and  the  diam- 
eters of  A,  B,  C,  and   D  are  16,  8,  20,   and    12  inches  respectively. 
Find  the  number  of  revolutions  made  by  D. 

2.  In  the  same  figure  let  A  represent  the  drive- wheel  of  an  engine 


PULLEYS.  53 

geared  by  belts  to  a  dynamo-pulley  Z>,  and  B  and  C  pulleys  on  a 
counter-shaft.  If  the  dynamo  makes  2000  revolutions  per  minute 
and  the  diameters  of  A,  B,  C,  andZ>  are  10  feet,  30  inches,  5  feet,  12 
inches,  respectively,  how  many  revolutions  per  minute  should  the 
engine-pulley  make  ? 

3.  In  the  same  figure  suppose  that  A  makes    100  revolutions  per 
minute,  and  that  D  is  to  make  3000.     The  diameters  of  A,  B,  and  C 
are  10  feet,  30  inches,  and  5  feet  respectively.     What  is  the  diameter 
of  the  pulley  to  be  put  on  the  dynamo  ? 

*  The  circumferential  speed  of  any  revolving  wheel  is  the  distance, 
in  feet,  passed  through  by  a  point  in  its  circumference  per  minute, 
and  is  equal  to  the  number  of  revolutions  per  minute  multiplied  by  the 
circumference  of  the  wheel  in  feet. 

4.  What  is  the  circumferential  speed  of  D  in  Problem  i  ? 

5.  What  is  the  circumferential  speed  of  A  in  Problem  i  ? 

6.  Suppose   that  D  in  Fig.  43  be  made  the  drive- wheel   of  an 
engine  making  150  revolutions  per  minute,  and  that  A,  B,  and  D  are 
20,  4,  and  20  inches  in  diameter  respectively.     What  diameter  should 
be  given  Cin  order  to  give  A  a  circumferential  speed  of  1000? 

*  The  circumferential  speed  of  the  pulley  equals  the  velocity  of  its  belt, 
there  being  no  slip. 


CHAPTER    VII. 
BELT-   AND    ROPE-GEARING. 

Belt-gearing  includes  all  appliances  concerned  in  trans- 
mitting motion  in  the  manner  of  a  belt  and  pulley;  such  as 
belts,  bands,  or  chains  running  on  pulleys  or  sprocket-wheels 
with  continuous  motion;  or  with  limited  motion,  as  where  a 
rope,  strap,  or  chain  passes  partly,  wholly,  or  several  times 
around  wheels  to  which  the  ends  are  made  fast,  as  in  the  case 
of  the  windlass.  Belt-gearing  is  very  desirable  especially  where 
a  uniform  velocity  of  driver  and  driven  wheel  is  not  required, 
because  of  its  noiseless  running,  lightness,  and  simplicity  of 
construction  as  compared  with  tooth-gearing,  link-gearing,  etc. 
In  cases  where  a  mathematical  relation  must  be  preserved 
between  the  speed  of  the  driving  pulley  and  the  speed  of  the 
driven  pulley,  the  sprocket-wheel,  .which  permits  no  slipping, 
is  used.  Belts  or  ropes  are  apt  to  slip  more  or  less.  The 
driving  power  of  a  belt  depends  mainly  upon  the  tightness 
with  which  it  is  stretched  around  the  pulley;  also  upon  the  arc 
of  contact,  and  upon  the  condition  of  the  belt  and  pulley-face 
with  regard  to  smoothness  of  surface. 

Leather  and  rubber  are  the  two  kinds  of  belting  most 
generally  used,  and  of  the  two  leather  will  usually  last 
longer. 

Leather  belts  may  be  single  or  of  any  number  of  layers 
cemented  together.  The  object  in  increasing  the  thickness  is 
to  increase  the  strength  without  increasing  the  width.  The 
best  leather  belts  are  made  of  oak-tanned  leather  curried  with 
the  use  of  tallow  and  cod-oil.  Such  belts  have  been  known 
to  continue  in  use  thirty  to  forty  years,  when  used  as 

54 


BELT-  AND  ROPE-GEARING.  55 

simple  driving-belts,  transmitting  a  proper  amount  of  power 
and  being  given  suitable  care.  The  hair  side  of  the  belt 
should  be  run  next  to  the  pulley.  It  has  been  found  by 
experiment  that  the  hair  or  grain  side  is  the  weaker.  The 
hair  side  will  also  crack  much  easier  than  the  flesh  side.  If 
the  grain  side  is  shaved  thin  and  stretched  a  little  a  large 
number  of  holes  can  be  seen,  showing  that  the  weakness  is 
probably  due  to  the  hair  having  had  root  on  that  side.  Again 
the  hair  side  is  smoother,  and  will  hug  the  face  of  the  pulley 
better,  and  this  is  a  condition  which  promotes  the  tractive 
force  of  a  belt.  When  a  belt  is  bent  around  a  pulley,  the  side 
of  the  belt  farthest  away  from  the  pulley  is  stretched,  while 
the  side  next  to  the  pulley  is  compressed.  It  is  plain,  then, 
that  the  flesh  or  stronger  side  should  be  on  the  outer  side, 
which  is  stretched,  while  the  hair  or  weaker  side  should  be 
placed  against  the  pulley,  where  there  is  not  so  much  strain. 

The  safe  working  tension  of  a  laced  belt  is  250  to  350  Ibs. 
per  square  inch  of  cross-section. 

When  the  driving  and  driven  pulleys,  Fig.  45,  are  at  rest 


FIG.  45.— Sag  of  Belt. 

the  tensions  in  the  two  halves  of  the  belt  will  be  the  same ;  but 
when  the  driver  rotates  in  the  direction  of  the  arrow,  the 
tension  on  the  tight  side  will  be  increased,  and  the  tension  on 
the  slack  side  will  be  diminished.  Let  7^  be  the  tension  on 
the  tight  side,  and  T2  the  tension  on  the  slack  side,  and  P  the 
effective  force  on  the  circumference  of  the  pulley;  then, 
P  —  Tv  —  Tr  Let  V  be  the  velocity  of  the  belt  in  feet  per 
minute ;  then  VP  =  the  number  of  foot-pounds  of  work  done 


56  MACHINERY  AND  MECHANICS. 

VP 
per  minute  and  H.P.  =__  -  —.      If  the  belt    passes   over  a 


pulley  D  feet  in  diameter,  that  makes  N  revolutions  per 
minute,  then  V  =  3.1416  X  D  X  N-  Substituting  this  value 
of  V  in  the  above  equation,  we  have, 

3.1416  X  D  X  NX  P 

ri.r.  "=• 


33OOO 

A  short  and  simple  rule  for  determining  the  horse-power 
that  will  be  transmitted  by  a  belt  is,  that  a  single  leather  belt, 
one  inch  wide,  travelling  1000  feet  per  minute,  will  transmit 
one  horse-power.  A  double  belt  one  inch  wide  travelling  600 
feet  per  minute  will  transmit  one  horse-power.  The  working 
stress  in  this  case  is  33  Ibs.  per  inch  of  width. 

Different  writers  give  other  figures  for  the  speed  of  belts 
necessary  to  transmit  one  horse-power.  The  rule  above  given, 
however,  is  a  very  safe  one  with  which  to  work. 

Mr.  F.  W.  Taylor  describes  in  the  Transactions  of  the 
American  Society  of  Mechanical  Engineers  a  series  of  experi- 
ments on  belting,  extending  over  nine  years.  His  results  give 
rise  to  principles  which,  if  adopted,  would  entail  heavier 
expense  than  is  usual  in  installations  of  belting.  The  rules 
are  on  this  account  not  much  used.  Among  other  things  he 
recommends  the  splicing  and  cementing  of  belts  in  preference 
to  lacings;  the  use  of  narrow,  thick  belts,  even  on  small 
pulleys,  in  preference  to  wide,  thin  belts  ;  and  that  the  thick- 
ness of  belts  should  be  increased  as  they  are  made  wider. 

A  belt  running  at  a  very  high  speed  will  have  its  effective 
driving  tension  diminished  by  the  tension  due  to  centrifugal 
force.  If  we  let  W  be  the  weight  of  one  foot  of  belt,  one  square 
inch  in  cross-section,  v  the  velocity  of  the  belt  in  feet  per  second, 
and  g  the  acceleration  due  to  gravity  =  32.  2,  then  the  centrifugal 
tension  Tc  may  be  found  as  f  Hows: 


BELT-  AND  ROPE  GEARING.  57 

The  weight    of    leather   per  cubic  foot   being   56  Ibs.,  the 
value  of  W  will  be  .388  Ibs.     Then 


32.2 

Subtracting  this  from  the  tension  per  inch  of  width  on  the 
tight  side,  will  give  the  effective  criving  tension  per  inch  of 
width. 

Rubber  belting  is  a  combination  of  rubber  and  cotton-duck, 
There  are  many  qualities  manufactured,  the  difference  in 
strength  depending  upon  the  quality  of  the  cotton-duck  used, 
as  the  tensile  strength  of  the  belt  is  in  this  fabric.  The  belt 
is  made  up  of  plies  of  cotton  cemented  together  with  rubber, 
and  the  entire  surface  covered  with  rubber. 

The  advantages  claimed  for  rubber  belting  are:  perfect 
uniformity  in  width  and  thickness  ;  it  is  not  affected  seriously 
by  excessive  degrees  of  heat  or  cold  ;  it  is  especially  adapted 
for  use  in  \vet  or  damp  places,  or  where  it  is  exposed  to  the 
action  of  steam  ;  and  it  is  less  liable  to  slip  on  the  pulley. 

A  comparatively  new  kind  of  belt  is  now  made,  called  the 
leather  link-belt,  which  is  considerably  used  for  heavy  work. 
It  consists  of  many  small  leather  links  fastened  together  with 
iron  *  rods,  as  shown  in  the  illustration,  Fig.  46.  The  rods 
run  through  the  holes  in  the  links  and  are  as  long  as  the  width 
of  the  belt.  It  is  devoid  of  the  usual  great  stiffness  which  is 
found  in  ordinary  belts  and  it  easily  adapts  itself  to  the  contour 
of  the  pulley,  no  matter  how  heavy  and  thick  it  may  be.  Its 
first  cost,  however,  is  an  objection  which  keeps  it  from  coming 
into  more  general  use. 

As  a  large  belt  runs  on  the  pulley,  a  cushion  of  air  is  made 
between  the  belt  and  pulley,  which  lessens  the  holding  power 
to  some  extent.  Some  belt  manufacturers  diminish  this 
cushioning  somewhat  by  perforating  the  belt  with  small  holes 
or  slits,  so  that  the  air  may  pass  through  and  allow  the  belt 
to  stick  close  to  the  pulley. 

Belts  will  hold  better  when  the  pulleys  are  at  long  distances 

*  Sometimes  leather  thongs. 


58  MACHINERY  AND  MECHANICS. 

apart  than  when  at  short  distances.  Belts  should  never,  if 
avoidable,  connect  two  shafts  one  of  which  is  directly  over  the 
other,  and,  in  general,  the  two  pulleys  should  have  a  position, 
such  that  there  may  be  a  sag  of  the  belt.  It  is  desirable  that 


FIG.  46. — Leather  Link-belt. 

the  angle  which  the  belt  makes  should  be  not  more  than  45 
degrees  with  the  horizontal. 

The  tensile  strength  of  the  solid  leather  belting  is  from 
2OOO  to  5000  Ibs.  per  square  inch;  but  only  about  1000  to 
1500  Ibs.  at  the  lacings.  The  working  strain  is  taken  at  not 
over  one  third  of  the  strength  of  the  lacing. 


FIG.  47. — Arrangement  for  Quarter-twist  Belt. 

Commonly  the  belt  connects  pulleys  that  are  on  parallel 
shafts,  but  this  is  not  necessarily  the  case.      Fig.  47  shows  the 


BELT-  AND  ROPE-GEARING.  59 

relative  position  of  the  pulleys  on  two  perpendicular  shafts 
which  gives  the  belt  a  quarter  twist.  In  this  case  the  belt 
must  run  squarely  onto  the  pulleys.  It  may  run  off  the  pulleys 
at  any  angle.  In  setting  pulleys  to  give  a  quarter  twist  to  a 
belt,  the  point  where  the  belt  leaves  the  driven  pulley  must 
be  in  the  central  plane  of  the  driving  pulley.  In  this  arrange- 
ment the  belt  can  run  in  only  one  direction.  If  an  attempt  is 
made  to  run  the  belt  in  the  reverse  direction  it  will  be  thrown 
from  the  pulleys.  Other  twists  may  be  given  by  the  use  of 
Guide-pulleys. 

Methods  of  Lacing. — The  effective  strength  of  a  belt,  as 
well  as  the  smoothness  and  uniformity  of  transmission,  depends 
on  the  manner  of  connecting  the  ends.  WJien  possible,  the 
belt  should  be  endless ;  that  is,  it  should  be  joined  together  in 
such  a  manner  that  the  strength  of  the  joint  shall  be  equal  to 
the  strength  of  the  belt  itself,  or  as  nearly  so  as  possible; 
also,  so  that  there  shall  be  no  extra  weight  caused  by  heavy 
lacing-leather.  The  heavy  joint  causes  a  vibratory  movement 
of  the  belt  when  running;  this  causes  variations  in  the  arc  of 
contact  and  this,  in  turn,  may  cause  the  belt  to  slip.  Where 
a  uniform  motion  is  required,  as  for  a  dynamo,  this  would  not 
be  admissible. 

The  two  methods  most  commonly  used  in  fastening  belting 
together  at  the  ends  are  the  Butt-joint  and  the  Lap-joint. 
With  the  butt-joint  and  especially  with  heavy  belts,  rawhide 
lacing  is  used.  With  smaller  belts,  wire  lacing  made  of  some 
pliable  composition  is  used  considerably.  This  makes  a  much 
less  clumsy  joint  and  less  waste  of  strength  by  the  punching 
of  holes  than  is  necessary  when  the  rawhide  lacing  is  used. 
The  lap-joint  is  made  by  beveling  or  scarfing  the  two  ends  and 
then  gluing  them  together,  under  pressure;  by  gluing  and 
riveting;  and  also  by  interlapping  the  different  plies,  when  the 
belt  is  not  single,  and  then  gluing.  The  lap-joint  is  best 
because  it  makes  practically  an  endless  belt. 

The  joints  in  rope  belting  are  made  similarly  by  inter- 
lapping  the  strands  or  fibres  and  then  wrapping  them  with 


6o 


MACHINERY  AND  MECHANICS. 


BEST  METHOD  OF  LACING  BELTING 


FIG.  48. — Butt-joint. 


FIG.  49. — Scarf-splice. 


BELT-  AND  ROPE-GEARING. 


61 


cords,  thus  making  a  strong  endless  rope  of  uniform 
size. 

When  the  distance  between  the  centres  of  two  shafts  and 
the  diameters  of  the  pulleys  are  given,  the  length  of  belting 
required  may  be  found  approximately  as  follows : 

RULE. — Add  the  diameters  in  feet  of  the  two  pulleys 
together^  divide  the  result  by  2  and  multiply  the  result  by 
3.1416.  Then  add  this  product  to  twice  the  distance  between 
the  centres  of  the  two  shafts. 


ROPE-DRIVIXG. 


When  rope  is  used  the  pulley  contains  a  groove  or  grooves 
in  its  face  in  which  the  rope  runs.  Rope  belting  is  commonly 
made  of  cotton,  hemp,  or  manila,  but  rawhide,  flax,  and 


FIG.  50. — Section  of  Pulley  for  Rope-drive. 

leather  are  sometimes  used.  With  small  pulleys  cotton  is  best 
as  it  is  softer  and  more  pliable,  and  there  is,  therefore,  less 
danger  of  breaking  the  fibres. 

The  principal  advantages  of  rope-driving  are  quiet  running 
and  convenience  in  application.  One  of  the  greatest  fields  of 
usefulness  for  rope-driving  is  in  the  transmission  of  power  to  a 
moderate  distance,  under  conditions  which  are  not  favorable 
to  the  use  of  leather  belting  or  shafting.  With  rope-driving 
one  is  enabled  at  a  comparatively  small  cost  to  transmit 
power  in  any  direction  to  a  building  remotely  situated  from 


62  MACHINERY  AND  MECHANICS. 

the  power,  which  would  otherwise  require  a  long  and  expen- 
sive line-shaft,  or  an  independent  engine  or  motor.  The 
facility  with  which  a  rope-drive  may  be  carried  in  any  direc- 
tion, across  rivers,  canals,  and  streets,  above  or  under  ground, 
up  or  down  hill,  over  houses  and  into  buildings,  is  a  feature 
which  recommends  rope  as  a  means  of  driving. 

The  ropes  most  commonly  used  are  from  I  to  2  inches  in 
diameter.  The  size  of  a  rope  is  very  often  given  by  its  cir- 
cumference or  girth.  The  tensile  strength  of  ropes,  for  rope- 
driving  varies  greatly,  though  it  is  generally  from  7000  to 
12,000  Ibs.  per  square  inch. 

The  weight  of  the  ropes  when  dry  is  given  approximately 
by  the  formula  W=  .$£P  =  .032  C2,  where  W  is  the  weight 
per  foot  of  length  and  D  the  diameter  and  C  the  circumference 
of  the  rope.  The  speed  of  driving  ropes  varies  from  1500  to 
7000  feet  per  minute. 

The  accepted  authority  on  rope-driving  in  this  country  is 
Mr.  C.  W.  Hunt.  He  allows  a  working-strain  on  a  i-inch 
rope  of  200  Ibs.  This  makes  the  working-strain  about  •£•$  of 
the  breaking  strength  of  the  rope.  This  strain  is  about  ^V  the 
strength  of  the  splice.  In  practice,  however,  this  limit  is  often 
greatly  exceeded,  on  account  of  vibrations  and  imperfect  ten- 
sion-adjusting devices. 

In  his  derivation  of  a  formula  for  horse-power,  he  used  a 
constant  driving-strain  on  a  I  -inch  rope  of  200  Ibs.,  and 
velocities  varying  from  10  to  140  feet  per  second.  The  driving- 
force  will  be  diminished  by  the  tension  due  to  centrifugal  force 
of  the  rope  passing  over  the  pulley.  Where  Tc  is  the  tension 
due  to  centrifugal  force,  J/Fthe  weight  of  rope  in  pounds  per 
foot,  v  the  velocity  of  rope  in  feet  per  second,  and  g  gravity, 


The  difference  between  Tc  and  the  maximum  tension  gives  the 
force  available  for  power  transmission.     As  a  certain  amount 


BELT-  AND  ROPE-GEARING. 


of  tension  is  necessary  on  the  slack  side  of  the  rope  to  give  it 
adhesion  to  the  pulley,  all  of  this  force  cannot  be  used.  As 
before,  let  TI  be  the  tension  on  the  tight  side,  and  T2  the  ten- 
sion on  the  slack  side.  Then  Ti-(T2  +  Tc)  is  the  effective 
driving  force.  Assuming  that  the  tension  on  the  slack  side 
of  the  rope  is  one-half  the  effective  driving  force  P,  we  have, 


Tl---Tc  = 


and 


Also,  the  tension,  T2,  on  the  slack  side  will  be 


Tc. 


The  tension  TI  will  increase  as  the  speed  is  raised,  since  Tc 
increases  as  the  square  of  the  velocity, 

With    the    foregoing  assumptions,   the  formula    for  horse- 
power may  now  be  stated 

HP        ™(T,- 
~ 


v  being  the  velocity  of  the  rope  in  feet  per  second. 

The  following  table  gives  the  horse-power  of  various  ropes 

r\i£ff*t-f*r\i-    c-r»£»p»r1c 


at  different  speeds. 


HORSE-POWER  OF  TRANSMISSION  ROPE  AT  VARIOUS  SPEEDS. 
(Computed  from  formula  given  above.) 


°    OS 

Speed  of  the  Rope  in  feet  per  minute. 

S-g^j 

]1 

iffi 

1500 

2000 

2500 

3000 

35°° 

4000 

4500 

5000 

OOOO 

7000 

8000 

* 

1-45 

1.9 

2-3 

2.7 

3 

32 

3-4 

3-4 

3-1 

2.2 

o 

20 

i 

2-3 

3-2 

3-6 

4.2 

4-6 

5-0 

5-3 

5-3 

4-9 

3-4 

o 

24 

I 

3-3 

4-3 

5-2 

5-8 

6.7 

7.2 

7.7 

7-7 

7-1 

4.9 

o 

30 

7 

4.5 

5-9 

7.0 

8.2 

9.1 

98 

10.8 

10.8 

9-3 

6.9 

o 

36 

I 

5.8 

7-7 

9.2 

10.7 

11.9 

12.8 

13-6 

13-7 

12.5 

8.8 

0 

42 

jj. 

9.2 

12.  1 

14-3 

16.8 

18.6 

20.0 

21.2 

21.4 

19-5 

13-8 

0 

54 

j| 

17-4 

20.7 

23.1 

26.8 

28.8 

3O.6 

30-8 

28.2 

19.8 

0 

60 

if 

18 

23.7 

28.2 

32.8 

36  4 

39-2 

41-5 

41.8 

37-4 

27.6 

o 

72 

2 

23.2 

30.8 

36.8 

42.8 

47-6 

51.2 

54-4 

54-8 

50 

35-2 

o 

84 

64  MACHINERY  AND  MECHANICS. 

For  very  light  work  and  for  guide-pulleys  the  rope  rests 
on  the  bottom  of  the  groove  in  the  pulley  {Fig.  50,  a),  but  for 
heavy  work  the  rope  works  in  a  groove  which  is  V-shaped 
(Fig.  50,  b),  whereby  the  holding  power  is  much  increased. 
Since  the  power  of  one  rope  is  limited,  and  as  it  is  not  con- 
venient to  use  very  large  ropes,  it  is  necessary,  in  most  cases, 
to  use  several  ropes.  The  pulleys  have  parallel  grooves  in 
which  the  ropes  are  placed,  sometimes  as  many  as  20  or  25. 

PROBLEMS. 

1.  A  leather  belt  is  ^  inch  thick  and  16  inches  wide.     What  ten- 
sile force  will  be  required  to  break  it  if  the  tensile  strength  of  leather 
is  3000  Ibs.  per  square  inch  ? 

2.  A  leather  belt   running  at  a  velocity  of  4000  feet  per  minute 
transmits  40  horse-power.     Find   the  driving  tension  P  on  the   cir- 
cumference of  the  pulley. 

3.  If  the  tension  on  the  tight  side  of  a  belt  is  twice  that  on  the 
slack  side,  find  Tl  and  T9  in  Problem  2. 

4.  If  the  safe  tension  per  inch  of  width  is  90  Ibs.,  find  the  width 
of  belt  required  in  Problem  2. 

5.  A   rope-pulley  is  20  feet  in  diameter  and  makes  500  revolu- 
tions per  minute  ;  find  the  velocity  of  the  rope. 

6.  A  rope  is  i  inch  in   diameter.      What  force  will  be   required 
to  break  it  if  the  tensile  strength  is  8000  Ibs.  per  square  inch  ? 

7.  Find  the  ciameter  of  each  of  the  13  ropes  which  crive  400  horse- 
power, the  velocity  of  the  ropes  being  4000  feet  per  minute.     See  table. 

8.  A  certain  drive  has  21  ropes  on  a  pulley  4  feet  in   diameter 
making  500  revolutions  per  minute.    What  horse-power  may  be  trans- 
mitted if  the  girth  of  the  ropes  is  3.14  inches? 

9.  What  is  the  weight  of  a  rope  which  is  2  inches  in  diameter  and 
10  feet  long? 

10.  A  dynamo  runs  at  1020  revolutions  per  minute  and  requires 
20  horse-power  to  operate  it.     The  power  is  furnished  by  an  engine 
running  at  150  revolutions  per  minute.    The  engine  drives  a  counter- 
shaft, which  in  turn  drives  the  dynamo.    If  the  pulley  on  the  dynamo 
is  12  inches  diameter  and  the  fly-wheel  of  the  engine  54  inches  dia- 
meter and  double  belts  are  used,  find  the  size  of  the  pulleys  on  the 
counter-shaft,  and  the  wilth  of  belts  necessary.     Assume  the  double 
belt  to  be  T5g  inch  thick. 


BELT-  xWZ>  ROPE-GEARING.  65 


11.  A  Corliss  engine  runs  at  85  revolutions  per  minute,  and  de- 
velops 1  86  horse-power.     If  the  main  line-shall  which  it  drives  runs 
at  235  revolutions  per  minute,  and  the  pulley  which  receives  the  power 
is  5  feet  in  diameter,  find  the  width  of  double   belt   used,  and  the 
diameter  of  the  engine  fly-wheel. 

12.  If  the  tension  on  the  slack  side  is  one  half  that  on  the  driving 
side  of  the  belt  in  Problem  n,  find  T^  and  7,.     Also  determine  the 
tension  due  to  centrifugal  force,  and  the  effective  driving  tension0 


OF    THE 

{   UNIVERSITY   ) 

OF 


CHAPTER   VIII. 
TOOTHED    WHEELS. 

TRANSMISSION  of  power  between  two  shafts,  by  means  of 
friction-wheels  and  belt-pulleys,  is  possible  only  so  long  as  the 
resistance  to  be  overcome  does  not  exceed  the  friction  which 
arises  at  the  circumference  of  the  wheels.  When  the  resist- 
ance exceeds  the  friction  a  slippage  will  occur.  To  prevent 
this  the  friction  must  be  made  greater,  in  one  case  by 
pressing  the  friction-wheels  closer  together,  and  in  the  other 
by  making  the  belt  tighter.  This  excessive  amount  of  pressure 
causes  a  corresponding  amount  of  friction  of  the  shafts  in  their 
bearings,  so  that  friction-wheels  cannot  be  employed  to  ad- 
vantage where  the  resistance  is  very  great,  especially  in  the 
case  of  slow-running  shafts. 

Neither  can  they  be  used  where  it  is  necessary  that  the 
speeds  of  the  two  shafts  have  an  exact  ratio  at  every  instant, 
as  in  screw-cutting  machines,  clocks,  etc.,  for  experience 
shows  that,  even  with  the  greatest  pressure,  friction-wheels 
and  belts  will  sometimes  slip.  To  overcome  these  difficulties 
the  toothed  wheel  is  used. 

Suppose  two  friction-  wheels  running  together  have  spaces 
cut  in  their  circumference  at  regular  intervals,  and  if  the 
material  from  these  spaces  be  placed  on  the  top  of  the  remain- 
ing solid  portion,  so  that  the  projections  of  one  will  fit  into  the 
depressions  in  the  other,  an  approximate  form  of  gear-wheel 
is  produced. 

66 


TOOTHED   WHEELS. 


The  original  diameter  of  the  disk  is  the  "  pitch  diameter  ", 
and  the  circumference  of  the  disk  itself  the  pitch-circle.  The 
portion  of  the  tooth  above  the  pitch-circle  is  known  as  the 
"face  "  or  addendum  of  the  tooth,  the  portion  below  as  the 


LINE 


FIG.  51. — Section  of  Gear-wheel. 

flank  or  dedendum.  The  distance  from  the  front  of  one  tooth 
to  the  front  of  the  next,  measured  on  the  pitch-circle,  is  known 
as  the  "circular  pitch,"  or  simply  as  the  "pitch."  Some- 
times the  pitch  is  given  as  the  number  of  teeth  per  inch  of 
pitch  diameter.  This  is  called  diametral  pitch.  Thus,  in  a 
wheel  of  36  teeth,  pitch  diameter  12  inches,  the  diametral 
pitch  is  3. 

Let  Pd  be  the  diametral  pitch  of  a  gear-wheel  of  pitch 
diameter  D\  let  the  circular  phch  be  Pc  and  the  number  of 
teeth  be  N.  Then 


N       3.1416 


pf= 


D  X  3-I4l6  _  3-14*6 

N  '  ~     ~  /»  ' 


68  MACHINERY  AND  MECHANICS. 

In  a  spur-wheel  (Fig.  51)  the  teeth  are  cut  in  the  surface 
of  a  cylinder  known  as  a  "blank"  (Fig.  53).  Spur-wheels 
transmit  motion  between  two  shafts  with  parallel  axes. 

Bevel-wheels  (Fig.  52)  are  formed  by  cutting  teeth  on  the 

surface  of  a  cone  or  frustum  of  a 
cone.  Bevel-wheels  transmit  mo- 
tion between  shafts  whose  axes 
intersect. 

Skew-wheels  are  formed  by 
cutting  'teeth  on  the  surface  of 
hyperboloids  of  revolution.  They 
transmit  motion  between  shafts 
which  do  not  intersect  and  which 
FIG.  52.— Bevel-gear.  are  not  in  the  same  plane. 

If  in  the  elementary  gear-wheel,  considered  earlier  in  this 
chapter,  the  teeth  were  made  in  the  form  of  rectangular  prisms, 
they  would,  in  running,  wear  themselves  to  approximate  forms 
of  either  one  of  two  curves,  the  epicycloid  or  the  involute  of  a 
circle.  In  the  practical  construction  of  gear-wheels  the  teeth 
are  cut  or  cast  in  the  shape  of  one  of  these  curves,  depending 
on  the  use  to  which  the  wheel  is  to  be  put.  The  teeth  of 
spur-gears  can  be  easily  cut  to  the  proper  form  in  the  milling- 
machine.  A  bevel-gear,  however,  cannot  be  perfectly  formed 
in  a  milling-machine,  as  the  thickness  of  the  teeth  constantly 
diminishes  toward  the  point  of  the  cone.  It  requires  a  special 
machine,  called  a  gear-shaper.  These  machines  plane  the 
teeth.  There  are  two  classes:  one  generates  the  tooth  itself 
as  it  planes  it,  such  as  the  Bilgram  planer;  the  second  class 
uses  a  former  or  template  which  guides  the  planing-tool,  such 
as  the  Fellows  gear-shaper. 

For  rough,  heavy  work  the  gears  are  cast  in  iron.  These 
are  known  as  Cast  Gears.  Gears  made  in  a  milling-machine 
or  gear-shaper  are  known  as  Cut  Gears.  Sometimes  in  very 
heavy  work,  as  in  transmitting  power  from  turbine-wheels, 
where  the  noise  is  intense  and  disagreeable,  one  of  the  gears 
is  provided  with  wooden  teeth  which  are  locked  in  place  by  a 


TOOTHED   WHEELS.  69 

simple  device.  These  diminish  the  noise  to  a  great  extent. 
Spur-gears  are  also  made  of  rawhide  or  leather,  where  it  is 
desired  to  diminish  noise.  The  leather  or  rawhide  is  com- 
pressed between  two  steel  or  brass  plates  and  then  is  cut  as 
an  ordinary  iron  gear. 

To   draw  all   the   teeth   on  a   spur-gear  would  be  a  very 
tedious  task  in  drafting.      To  save  time,  therefore,  gears  are 


American  XacMnitt 


CUTTER  BLANK 

FIG.  53. — Fellows  Gear-cutter  and  Partially  Developed  Gear. 

usually  represented  by  their  pitch-circles  (see  Fig.  54).  They 
are  also  shown  as  blanks,  in  which  a  few  teeth  have  been  cut, 
the  teeth  on  each  blank  being  in  mesh. 

In  making  gear-wheels,  the  space  is  made  slightly  greater 
than  the  thickness  of  the  tooth.  This  is  necessary  in  order 
that  the  teeth  shall  not  bind  on  each  other  when  running. 
It  is  the  aim  of  all  designers  to  make  this  "backlash"  as 
small  as  possible.  The  depth  of  the  space  is  also  made  a  little 
greater  than  is  absolutely  necessary.  The  extra  distance  in 
this  case  is  termed  the  "clearance." 

The  width  of  the  gear  is  termed  the  "face.  It  is 
generally  made  from  two  to  three  times  the  circular  pitch. 
Grant's  "  Gear  Book,"  in  a  list  of  stock  gears,  gives  a  face  of 
3  to  4  inches  for  a  gear  of  3  diametral  pitch,  —  1.047  inches 
circular  pitch,  and  i  to  f  inch  for  a  gear  of  20  diametral 


1o  MACHINERY  AND  MECHANICS. 

pitch,     =0.157    inch    circular   pitch.      Another   manufacturer 
gives  the  face  as  i^  inches  for  a  circular  pitch  of  £  inch,  and 


various  figures  up  to  a  circular  pitch  of  6  inches,  where  the 
face  is  20  inches. 

In  the  section  of  a  gear-wheel  shown  in  Fig.  5 1  the  fol- 
lowing are  the  dimensions: 

Pitch   (circular)  =  /  =  arc   abc\  face  =  2.5/5  thickness  of 


TOOTHED  WHEELS. 


tooth  '•=  arc  be  =  -47/;  space  =  arc  ab  =  -53/;  total  height 
of  tooth  =  h  =  .//;  addendum  =  s  =  .$p\  dedendum  =  d 

=  -4A 

In  terms  of  diametral  pitch,  Pd\ 


An  Inside  or  Annular  Gear  is  a  wheel  with  gear-  teeth  cut 
on  the  inside  of  the  rim  as  shown  in  Fig.  55.      It  works  in 


FIG.  55. — Annular  Gear. 

connection  with  a  pinion  (a  small  spur-gear),  and  the  same 
considerations  as  to  form  and  dimensions  apply  as  in  spur- 
wheels. 

A  Rack  is  a  straight  rectangular  piece  of  metal  in  which 
teeth  have  been  cut.  It  is  used  to  convert  rotary  into  recip- 
rocating motion  or  vice  versa  by  means  of  a  pinion.  The 


7*  MACHINERY  AND  MECHANICS. 

teeth  may  be  either  of  the  involute  or  epicycloidal  system. 
An  illustration  of  a  rack  and  pinion  is  given  in  Fig.  79. 

The  same  relations  as  regards  diameters  and  revolutions 
exist  in  gear-wheels  as  in  pulleys.  But  for  the  diameter  of  the 
wheels  the  number  of  teeth  may  be  substituted. 

Let  N  and  n  be  the  number  of  teeth  on  wheels  of  diameter 
D  and  d,  making  R  and  r  revolutions  respectively ;  then 

rn  rn  RN  RN 

R*N=rXn-     ^  =  ^;     ^=^',     r=~;     n=  — . 

If  a  system  of  gear-wheels  is  used  to  transmit  motion  from 
a  driver  to  a  follower,  the  intermediate  gears  may  be  neglected 
in  calculating  the  relative  velocities  of  the  driver  and  followers; 
the  driver  and  follower  may  be  considered  as  if  theytrjaelshed 
directly  into  one  another. 

A  train  of  gears  and  pinions  (Fig.  56)  is  a  train  in  which 


FIG.  56. — Train  of  Gears  and  Pinions. 

a  gear  drives  a  pinion  rigidly  fastened  to  a  gear  on  the  same 
axis,  which  gear  in  turn  drives  another  pinion,  which  may  or 
may  not  be  attached  to  another  gear.  If  the  number  of  teeth 
in  each  of  the  gears  and  each  of  the  pinions  is  given,  together 
with  the  number  of  revolutions  of  the  first  driver,  the  number 
of  revolutions  of  the  last  follower  may  be  obtained  as  follows: 

Multiply  the  diameters,  or  the  circumferences,  or  the  number 
of  teeth  of  all  the  drivers  together,  and  this  product  by  the 
number  of  revolutions  of  the  first  wheel;  divide  this  product  by 
the  continued  product  of  the  diameters,  or  the  circumferences, 
or  the  number  of  teeth  of  all  the  followers.  The  quotient  is 
the  number  of  revolutions  of  the  last  follower. 


TOOTHED    WHEELS  7J 

In  regard  to  power  transmitted  by  gear-teeth,  authorities 
vary  greatly  as  to  the  formulae  which  should  be  used.  All 
formulae  for  determining  the  horse-power  transmitted  by  gear- 
ing may  be  reduced  to  one  of  three  forms  : 

H.P.  =  CVpf    or     CVf     or     CVff, 

in  which  C  is  a  coefficient,  /  the  pitch  in  inches,  V  the  velocity 
of  the  pitch-line  in  feet  per  second,  and  /"the  face  of  the  tooth 
in  inches. 

The  following  is  a  formula  of  the  first  style  : 
Let  P  =  driving  force  at  pitch-line  in  pounds  ; 
D  =  diameter  of  pitch-circle  in  inches  ; 
V  —  velocity  of  pitch-line  in  feet  per  minute; 
N  —  number  of  revolutions  per  minute  ; 
H  =  horse-power  transmitted  by  wheel  ; 
f  •=  face  of  tooth  in  inches; 
/  =  pitch  of  teeth  in  inches. 
Then 

PV 

H=—  (I) 

33,000'  v  * 

ana  V  = 


12 
Substituting  this  value  of  V  m  (i),  we  have 


33,000  x  12 


. 


An  average  value  of  P  from  different  authorities  is 
Substituting  this  value  of  P  in  (2),  we  have 


Prof.   Harkness  gives  H.P.  =  — - ~-  - ,   where 

Vi  +  0.65  F 

velocity  in  feet  per  second. 


74  MACHINERY  AND  MECHANICS. 


PROBLEMS. 

1.  In  Fig.  56  A  has  80  teeth,  B  has  20,  C  has  60,  D  has  30,  E 
has  40,  and  F  has   10.      If  A  makes  50  revolutions  per  minute,  how 
many  does  F make  per  minute?  Ans.    1600. 

2.  In  the  same  figure  suppose  that  A  and  /'make  200  and  4000 
revolutions  respectively  per  minute,  and   that  B.  E,  and  F  have  50, 
40,  and  30  teeth  respectively,  what  may  be  the  number  of  teeth   on 
each  of  the  other  wheels  ? 

3.  Required  the  diameter  of  a  spur-wheel  which  has  100  teeth  and. 
a  pitch  of  1.57  inches.  Ans.    50  inches. 

4.  How  many  teeth  in  a  wheel    10  inches  in  diameter,  the  pitch 
being  .2618  inches  ?  Ans.    120. 

5.  Required  the  pitch  of  a  wheel  of  100  teeth,  the  diameter  being 
12  inches.  Ans.    .3770  inches. 

.  6.  A  certain  spur-wheel  has  40  teeth  and  its  diameter  is  10  inches. 
Find  the  pitch,  thickness  of  teeth,  width  of  space,  total  height  of 
tooth,  height  above  pitch-line,  and  depth  below  the  pitch-line. 

7.  What  is  the  diameter  of  the  face  circle  in  the  above  problem? 

8.  What  is  the  diametral  pitch  of  a  spur-wheel  of  100  teeth  having 
a  diameter  of  10  inches? 

9.  What  is  the  diameter  of  the  pitch-circle  in  the  above  problem, 
also  the  thickness  of  the  teeth  ? 

10.  What  would  be  the  diameter  of  a  blank  to  be  used  in  making 
a  cut  gear  whose  pitch-circle  is  to  be  6   inches   in   diameter  and  the 
pitch  J  inch  ? 

11.  What  horse-power  will  be  transmitted  by  a  spur-wheel  3  feet 
in  diameter  making  200  revolutions  per  minute,  the  pitch  of  the  teeth 
being  2  inches? 

12.  It  is  desired  that  a  spur-wheel  with  a  diameter  of  24  inches 
shall    transmit    10   horse-power    while    making    100    revolutions   per 
minute.     What  should  be  the  pitch  of  the  teeth  ? 


CHAPTER   IX. 
THE   SCREW. 

THE  screw  is  a  combination  of  the  lever  and  the  inclined 
plane,  and  the  mechanical  advantage  depends  both  on  the  arm 
of  the  working  lever  and  the  inclination  of  the  thread  or  inclined 
plane  which  supports  the  weight. 

The  efficiency  of  the  screw  is  very  low,  from  15  to  45  per 
cent.  A  large  amount  of  the  force  applied  is  lost  in  friction 
in  the  nut.  If  the  faces  of  the  threads  are  inclined,  as  in  a 
V  thread,  the  friction  is  greater  than  for  a  square  thread.  The 
efficiency  increases  if  the  pitch,  or  distance  between  two  con- 
secutive threads,  is  increased. 

Applications  of  the  screw  may  be  seen  in  the  jack-screw, 
the  vise,  bolts,  nuts,  etc.  The  jack-screw,  Fig.  57,  is  a 
machine  for  raising  heavy  weights.  It  consists  of  a  screw  to 
which  is  attached  a  lever  for  applying  force,  and  a  heavy  base 
A,  having  screw-threads  on  the  inside.  When  the  handle  is 
turned,  the  screw  moves  up  or  down,  according  to  the  direc- 
tion of  rotation  of  the  handle.  The  weight  is  placed  on  the 
head  B,  which  does  not  turn  with  the  screw,  thus  allowing  the 
weight  to  move  up  without  rotation.  The  equation 

*  ,F  X  2  X  3-  Hi6  X  ^  =   Wx  pitch  X  (/+  i) 

gives  the  relation  of  the  Weight  to  the  applied  force,  in  which 
F=  force  applied,  W=  weight,  R  =  radius  of  handle,  and 
f—  coefficient  of  friction  of  the  screw.  This  relation  is  derived 
by  the  application  of  the  Law  of  Machines,  Chapter  I.  With 
one  turn  of  the  handle  the  applied  force  moves  around  the 

•The"  Efficiency  "  =  ^  X  Pitch 


2X  3-  1416  XJ? 

75 


76 


MACHINERY  AND  MECHANICS. 


circumference  of  a  circle,  the  radius  of  which  is  the  length  of 
the  handle.  To  find  the  circumference  when  the  radius  is 
given,  multiply  the  radius  by  2  X  3.1416.  If  we  denote 
radius  by  R,  we  have  2  X  3.1416  X  R  as  the  distance  moved 
through  by  the  applied  force  during  one  turn  of  the  handle. 
During  this  one  turn  of  the  handle  the  weight  is  lifted  through 


L    _ 

sj 

\-S-Y 

->  o   ( 

FIG.  57. — Jack-screw. 

a  distance  equal  to  the  length  in  the  direction  of  the  axis  of  a 
thread  plus  a  space;  this  length  is  called  pitch. 

The  endless  screw,  or  worm,  is  a  combination  of  the  screw 
with  a  worm-wheel.  The  worm  is  secured  in  bearings  so  that 
it  cannot  move  in  the  direction  of  its  length.  The  threads  of 
the  screw  mesh  with  the  teeth  of  the  worm-wheel,  and  this  in 
turn  may  impart  motion  to  a  train  of  wheel-work. 

In    Fig.    58  the    force    is    applied    by  means   of  a  crank, 


THE  SCREW. 


77 


though  a  pulley  could  be  used,  instead  of  a  crank,  and  belted  to 
an  engine  or  shaft. 

Fx    2  X  3-i4i6  X  R  =  Wv  X  pitch 

is  the  equation  of  work  for  the  screw  part  of  the  machine  alone. 
By  solving  for  Wl  we  find  that  the  screw  will  raise  a  weight 

Fx  2  X  3-HI6  X  R 

w  — 

1  Pitch 

This  weight  W^  in  its  turn,  acts  as  a  turning  force  against  the 
circumference  of  the  worm-wheel  at  A ,  so  that  we  may  now 


FIG.  58. — Endless  Screw. 

regard  it  as  force  to  be  used  in  turning  the  wheel  against  the 
resistance  offered  by  the  weight  which  hangs  on  the  smaller 
wheel  B.  Let  Rl  be  the  radius  of  the  large  wheel  A,  and  R2 
the  radius  of  the  small  wheel  B.  Then,  multiplying  the  force 
W^  by  its  lever-arm  Rl ,  and  the  weight  by  its  lever-arm  R2 , 
we  have 

FX2  X  3-1416  X  R  . 


Pitch 


R 


or 


W= 


3-1416  xRxRl 


Pitch  X  R. 


The  relation  of  the  angular  velocities  of  the  crank  R  and 
the  worm-wheel  A  is  shown  in  the  equation  R  =  N  X  r,  in 
which  R  and  r  represent  the  number  of  revolutions  of  the  crank 


MACHINERY  AND  MECHANICS. 


R  and  the  wheel  A,  respectively,  and  N  the  number  of  teeth 
on  the  worm-wheel. 

Screw-threads. — Screw-threads  are  employed  for  two  pur- 
poses, one  of  which  is  holding  or  securing,  and  the  other 
transmitting  motion.  Examples  of  the  former  are  bolts,  nuts, 
screws,  etc.  ;  of  the  latter,  endless  screws  and  the  screw  on  the 
engine-lathe  for  moving  the  tool-carriage. 

Fig.    59    shows    the    Sellers    or    United    States    standard 


FIG.  59. — United  States  Standard  Thread. 

thread,  which  is  used  principally  in  the  United  States.  It  will 
be  noticed  that  the  V-shaped  threads  are  flattened  a  little  at 
the  top  and  bottom.  The  amount  of  flat  is  given  by  the 

equation  /"=•'-    —\  in  which  f  is  the  width  of  flat  and  n  is 

the  number  of  threads  to  the  inch.  This  makes  a  solid 
sound  thread  avoiding  the  broken  edges  which  are  often  the 
result  if  the  sharp  edge  is  permitted.  The  sides  of  the  thread 
make  an  angle  of  60  degrees  with  the  axis  of  the  thread,  as 
shown  in  the  figure. 

SCREW-THREADS,    UNITED    STATES   STANDARD. 


Diam. 

Pitch. 

Diam. 

Pitch. 

Diam. 

Pitch. 

Diam. 

Pitch. 

Diam. 

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ft 

II 

THE  SCREW. 


79 


The  relation  between  the  pitch  P  and  the  diameter  D  of 
the  U.  S.  standard  thread  is  given  approximately  by  the 
formula 

P=  .24  VD-\-  .62$  —  .175. 

The  Whitworth  or  English  standard  thread  is  shown  in 
Fig.  60.  The  sides  of  the  threads  make  an  angle  of  55  degrees 


FIG.  60. — Whitworth  Screw-thread. 

with  each  other,  and  the  bottom  and  top  of  the  thread  is 
rounded.  Fig.  6 1  shows  a  square  thread,  a  part  of  which  is 
right-handed  and  part  left-handed. 


RIGHT 


LEFT 


FIG.  61. — Square  Thread. 

The  diameter  of  a  thread  is  the  largest  diameter  measured 
perpendicular  to  the  axis  of  the  screw.  The  depth  of  thread 
is  the  vertical  height  of  the  tooth  above  the  bottom.  The  pitch 
of  the  thread  is  the  distance  taken  up  by  one  thread  on  the 
axis.  For  a  square  thread  the  pitch  would  consist  of  a  thread 
and  a  space.  The  size  of  thread  is  generally  designated  as  so 
many  threads  to  the  inch.  Screw-threads  on  the  outside  of  a 
cylinder,  as  threads  of  a  bolt,  are  called  male  threads,  and  the 
threads  on  the  inside,  as  the  threads  in  a  nut,  are  called  female 
threads. 


8o 


MACHINERY  AND  MECHANICS. 


Screw-threads  are  made  with  taps,  dies,  lathes,  and  special 
screw-cutting  machines.  The  tap  is  used  for  making  inside  or 
female  threads,  and  the  die  for  making  the  outside  or  male 
threads,  while  either  kind  of  thread  may  be  made  in  the  lathe. 
In  threading  bolts  and  piping,  different  sets  of  taps  and  dies 
must  be  used,  the  pipe-thread  always  being  smaller  and  of 
greater  number  to  the  inch  than  those  on  the  bolt  or  screw. 
They  also  taper  toward  the  end  of  the  pipe.  For  this  reason, 
we  have  what  is  known  as  the  bolt  or  standard  dies  and  taps, 
and  pipe  dies  and  taps.  For  example,  the  number  of  threads 
per  inch  on  a  i-inch  bolt,  U.  S.  standard,  is  8,  while  the 
number  of  threads  per  inch  on  a  i-inch  pipe  is  11.5.  The 
reason  for  making  more  threads  on  a  pipe  is  that  by  making 
more  of  them  the  depth  of  each  thread  is  made  less,  hence 
there  is  less  danger  of  cutting  through  the  thin  pipe. 

Bolts. — Bolts  are  made  of  wrought  iron  or  steel  and  are 
forged  out  by  bolt-making  machines,  and  the  threads  put  on  with 
dies  or  with  special  thread-cutting  machines.  The  machine- 
bolt^  Fig.  62,  may  have  either  a  square  or  a  hexagonal  head 


FIG.  62. — Machine-bolt. 

with  nut  to  match.      The  carriage-bolt,  Fig.  63,   differs  from 
the  machine-bolt  mainly  in   having  a  round  or  oval  head  and 


FIG.  63. — Carriage-bolt. 

being  square  in  cross-section  for  a  short  distance  under  the 
head,  and  generally  has  a  square  nut.      The  stove-bolt,    Fig. 


THE  SCREW. 


81 


64,  has  a  countersunk  head  with  a  slot  sawed  in  it  for  the  use 
of  a  screw-driver.      A  cotter-bolt  or  split  pin  is  split  along  its 


FIG.  64. — Stove-bolt. 

axis ;  the  split  portions  are  bent  at  right  angles  to  the  axis, 
thus  doing  away  with  screw-threads  and  a  nut.      The  stud-bolt 


FIG.  65.— Stud. 

has  no  head,  but  screws  directly  into  the  piece  which  it  is  to 
hold,  a  nut  being  used  on  the  end ;  an  example  may  be  seen 
on  the  cylinder-head  of  an  engine.  An  eye-bolt  is  one  having 
an  eye  instead  of  a  head. 

Screws. — Fig.   66  represen  s  a    cap-screw.      It  takes  the 


Fiv;.  66.— Ca^ -31  rew. 

place  of  a  bolt,  and  screws  into  one  of  the  pieces  to  be  held, 
the  shoulder  or  cap  on  the  end  of  the  screw  giving  it  the  hold- 


FIG.  67. — Lag-screw. 

ing  power.      The  lag-screw,  Fig.  67,   is  used  in  wood  only, 
usually  for  hanging  shafting.     Fig.  68  represents  a  drive-screw, 


8z  MACHINERY  AND  MECHANICS. 

and  Fig.  69  the  common  wood-screw.     The  wood-screw  may 
have  a  round  or  a  flat  head.     The  set-screw  is  one  in  which 


FIG.  68. — Drive-screw. 


FIG.  69. — Wood-screw. 

the   holding   power   is  produced  by  the   pressure   of  the   end 
against  a  piece  of  work.      The  end  is  hardened. 


PROBLEMS. 

1.  What  weight  will  be  raised  by  a  jack-screw,  if  its   handle  is  20 
inches  long,  the  pitch  of  the  threads  J  inch,  and  the   force  applied 
130  Ibs.,  neglecting  friction?  Ans.   75,398.4  Ibs. 

2.  Design  a  jack-screw  that  will  raise  a  weight  of  20,000  Ibs. 
with  an  applied  force  of  100  Ibs.,  the  length  of  the  handle  being    10 
inches,  neglecting  friction.  Ans.   Pitch  =  .31416  inches. 

3.  What  force  must  be  applied  in  order  to  raise  a  weight  of  12,000 
Ibs.   if  the  handle   is  16  inches  in  length,  and  the  pitch  of  the  thread 
\  inch,  neglecting  friction?  Ans.    60  Ibs.  about. 

4.  Design  a  jack-screw  that  will  raise  a  weight  of  1600  Ibs.  with 
an  applied  force   of  100  Ibs.,  taking  the  efficiency  to  be  30  per  cent 
on  account  of  friction. 

5.  What  weight  can  be  raised  with  an  endless  screw,  arranged  as 
in  Fig.  58,  if  the  length  of  the  handle  is  20  inches,  the  pitch  of  the 
threads  \  inch,  the  radius  of  the  worm-wheel  A  10  inches,  and  the 
radius  of  the  small  wheel  B  5  inches,  the  force  applied  at  the  end  of 
the  handle  being  100  Ibs.,  the  efficiency  being  50  per  cent  ? 

6.  What  must  be  the  length  of  the  handle  of  an  endless  screw  in 
order  that  a  weight  of  4000  Ibs.  may  be  raised  by  a  force  of  100  Ibs., 
the  other  dimensions  and  efficiency  being  the  same  as  for  problem  5  ? 


THE  SCREW.  83 

7.  Design  an  endless  screw  similar  to  the  one  shown  in  Fig.  58 
which  will  raise  a  weight  of  8000  Ibs.  with  a  force  of  100  Ibs.,  neg- 
lecting friction. 

8.  In   Fig.   58,  how  many  revolutions  will  A  make  if  A  has  20 
teeth  and  R  makes  200  revolutions  per  minute  ? 

9.  How  many  revolutions  of  the  crank  in  the  above  arrangement 
will  be  required  in  causing  A  to  make  3  revolutions? 

10.  What  should  be  the  pitch  of  the  threads  for  a  bolt  2  inches  in 
diameter  ? 


CHAPTER   X. 
CAMS. 

THE  Cam  is  a  revolving  inclined  plane.      It  may  be  either 
an  inclined  plane  wrapped  around  a  cylinder,  as  in  Fig.  70,  or 


FIG.  70. — Cam, 

it  maybe  an  inclined  plane  curved  edgewise,  as  in  Fig.  71. 
This  mechanism  is  generally  used  for  the  purpose  of  producing 
a  reciprocating  motion  in  rods  and  levers  by  giving  the  cam  a 
rotary  motion.  In  Fig.  72,  BCD  represents  the  cam  turning 
on  the  axis  A,  and  giving  a  reciprocating  rectilinear  motion  to 
the  heavy  rod  EF,  which  is  constrained  to  move  in  its  recti- 
linear path  by  the  guide-rollers.  The  rotation  of  the  axis 
being  in  the  direction  of  the  arrow,  the  rod  EF  has  an  upward 
motion  until  the  extreme  point  B  of  the  cam  comes  in  line 
with  the  rod,  when  the  portion  BG  of  the  cam  allows  the  rod 

84 


CAMS. 


to  fall  by  its  own  weight  or  by  the  action  of  a  spring  until 
the  point  G  comes  in  line-with  the  rod,  and  so  on ;  thus  one 
revolution  of  the   cam  here  presented  will  cause  the  rod  to 
make    three    upward    and     three 
downward  strokes. 

Within  certain  limits  the  use 
of  cams  admits  of  the  certain  trans- 
mission, from  a  uniformly  revolv- 
ing shaft,  of  widely  varying  veloci- 
ties and  in  an  easily  determined 
manner.  For  this  reason  they  are 


r\ 


/~\ 


3 

3] 


FIG.  71. — Cam. 


FIG.  72. — Cam  and  Follower. 


often  convenient.  By  varying  the  curve  of  the  cam  any  law 
of  motion  may  be  given  to  the  rod.  The  rod  Ft  Fig.  72,  is 
called  the  follower,  and  is  generally  provided  with  a  roller  as 
shown  in  the  cut,  by  means  of  which  the  contact  between  the 
cam  and  the  follower  is  changed  from  a  sliding  contact  to  a 
rolling  contact,  thus  lessening,  to  some  extent,  the  friction  and 
wemr.  The  use  of  a  cam  is  accompanied  by  a  very  large 
amount  of  friction  due  to  the  contact  of  the  follower  and  the 
driver,  especially  where  it  is  not  possible  to  use  a  roller  on  the 
follower.  This  causes  a  wear  of  the  parts,  which  in  time 
makes  a  backlash  and,  with  high  speeds,  much  noise.  The 
cam  is  the  mechanical  movement  that  the  designer  usually  calls 
to  his  aid  as  the  last  resort,  after  having  failed  to  obtain  the 
necessary  motion  of  a  piece  by  other  means  which  would  have 
made  lighter  and  quieter  running  parts.  The  cam  is,  how- 


MACHINERY  AND  MECHANICS. 


ever,  a  very  useful   movement,  and  in  certain  cases  must  be 
accepted,  though  it  is  to  be  avoided  where  possible. 

The  path  of  the  follower  may  be  a  straight  line,  a  circle 
or  any  other  curve.  Fig.  73  illustrates  a  cam  with  a  swinging 
follower.  In  this  case  the  path  of  the  point  D  of  the  follower 
will  be  the  arc  of  the  circle  EF. 

In  some  cam  movements  the  follower  has  a  flat  bearing- 
piece,  Fig.  74,  instead  of  a  point, 
which  for  the  same  cam  changes  the 
law  of  motion  of  the  follower,  but 
gives  a  more  extended  bearing  sur- 
face to  the  cam.  It  is  called  a  flat- 
footed  follower.  Cams  often  have 
grooves  in  their  perimeters  for  the 
purpose  of  confining  the  follower  to 
its  proper  path. 


FIG.  73. — Cam  with  Swinging 
Follower. 


FIG.  74. — Cam  and  Flat-footed 
Follower. 


To  find  the  curve  forming  the  edge  of  the  cam  so  that  the 
velocity  ratio  of  the  rod  and  the  axis  of  the  cam  may  be  constant: 

In  Fig.  75  let  A  be  the  centre  of  the  cam.  From  A  as 
a  centre  with  any  convenient  distance  AC  as  a  radius  describe 
the  circle  CEDBN.  On  BA  take  Ba  equal  to  the  length  of 
the  stroke  of  the  rod ;  divide  it  into  any  number  of  equal  parts, 
say  five,  in  the  points  b,  c,  d,  e,  and  divide  the  semicircle 
BDEFG  into  the  same  number  of  equal  parts  by  the  radial  lines 
AD,  AE,  AF,  and  AG.  From  A  as  a  centre  with  Ab,  Ac,  Ad, 
and  Ae  as  radii  describe  the  dotted  arcs  cutting  AD,  AE, 
etc.,  at  the  points  s,  k,  I,  m\  then  through  these  points  draw 


CAMS. 


the  curve  asklmpn.  This  curve  is  the  Spiral  of  Archimedes. 
The  peculiarity  of  this  curve  is  that  a  point  following  it  will 
move  outward  radially  equal  distances  when  passing  through 


equal  angles.  All  lines  drawn  through  the  centre  A  of  this 
curve  are  equal :  thus  aC  equals  In  =  sp.  Hence  if  the  rod 
had  two  pins  placed  at  a  and  C,  the  cam  would  revolve  between 
them,  and  would  cause  the  rod  to  make  a  downward  as  well 
as  an  upward  stroke. 


88 


MACHINERY  AND  MECHANICS. 


The  following  example  *  gives  a  solution  of  the  cam  and 
follower  in  which  the  cam  has  a  variable  velocity  of  revolution 
about  its  axis,  and  the  follower  moves  through  a  given  desired 
curve.  In  Fig.  76  let  D  be  the  follower,  a  part  of  which  is 
left  out  of  the  figure.  A  is  to  be  the  centre  of  rotation  of  the 
cam,  and  it  is  desired  that  the  path  of  the  follower-point  be  a 

curve  I  2345.  To  find  the  curve 
of  a  cam  necessary  to  fill  these  con- 
ditions, proceed  as  follows :  For 
convenience  cut  a  templet  to  the 
follower-path  12345  with  the 
centre  point  A  marked.  Then 
with  the  angles  iA2,  2A$,  etc., 
FlG<  76.  laid  off  according  to  the  velocities 

during  their  part  of  the  stroke,  the  several  curves  may  be  struck 
by  the  templet.  Now  drawing  in  the  arcs  from  the  points  I, 
2,  3,  etc.,  of  the  follower-path,  we  obtain  intersections  and 
can  draw  the  curve  1234,  etc.  This  is  called  the  method  of 
intersections  and  is  the  one  usually  employed  in  practice. 

Cams  are  often  used  on  engines  for  giving  the  proper 
movements  to  valves.  Fig.  77  shows  a  cam  movement  some- 
times used  in  operating  shearing-  and  punching-machines. 
The  cam  revolves  about  its  axis  O,  presses  against  the  under 
side  of  the  lever  A,  thus  causing  an  upward  and  downward 


FIG.  77. — Shear  operated  by  a  Cam.  FIG.  78. 

movement  of  the  shear.     The  inverse  cam  is  a  movement  in 
which  are  the  elements  of  the  grooved  cam  and  follower,  but 

*  Robinson's  "  Principles  of  Mechanism." 


CAMS.  89 

where  the  driver  has  the  pin  or  roller  and  where  the  follower 
has  a  groove.  It  is  sometimes  called  the  pin  and  slit.  An 
example  is  shown  in  Fig.  78,  in  which  the  slotted  piece  B  is 
the  follower  and  A  the  driver. 

The  relation  of  the  applied  force  to  the  resistance  is  calcu- 
lated for  cams  in  the  same  manner  as  in  the  case  of  the  screw ; 
that  is,  by  the  application  of  the  Law  of  Machines.  In  Fig.  72 
let  the  length  of  the  handle  be  R.  Let  AC  —  AH  =  d  =  the 
distance  through  which  the  follower  is  lifted.  The  follower 
will  make  three  movements  for  each  revolution  of  the  cam; 
hence,  applying  the  Law  of  Machines,  we  have 

Fx  2  X  3-HI6  X  R  =  IV  x  3  X  d 

as  the  equation  of  work,  /''being  the  force  applied  and  IV  the 
weight  of  the  follower.  This  of  course  applies  only  where 
friction  is  neglected. 


CHAPTER   XI. 
THE   LEVER   AND   SOME   OF   ITS   MODIFICATIONS. 

As  has  been  stated  before,  the  lever  and  its  modifications 
make  up  a  large  part  of  the  mechanism  of  much  of  the 
machinery  now  used,  different  methods  of  using  it  being 
employed  as  may  be  convenient.  A  crow-bar  is  an  excellent 
example  of  the  lever.  Examples  are  also  seen  in  the  rack 


FIG.  79. — Rack  and  Pinion. 

and  pinion,  the  pulley,  the  wheel  and  axle,  cranes,  etc.,  the 
action  of  the  lever  in  these  last-named  cases  being  continuous. 
Law  of  the  Lever. —  The  applied  force  multiplied  by  its 
distance  from  the  fulcrum  equals  the  weight  multiplied  by  its 
distance  from  the  fulcrum. 

90 


THE  LEVER  AND  SOME  OF  ITS  MODIFICATIONS. 


Fig.  79  shows  the  rack  and  pinion.  In  this  arrangement 
the  lever-arm  of  the  applied  force  is  the  length  of  the  crank 
FM,  and  the  lever-arm  of  the  resistance  is  the  radius  FN  of 
the  pitch-circle  of  the  pinion. 

The  Moving  Strut  and  the  Toggle-joint  are  two  applica- 
tions of  the  lever.  The  moving 
strut  consists  of  a  bar,  Fig.  80, 
which  rests  against  some  projec- 
tion. The  weight  IV  to  be  moved 
rests  on  a  plane,  and  the  extrem- 
ity of  the  bar  is  placed  against  it. 
If  a  force  P  be  applied  in  the  direc- 
tion of  the  arrow,  the  strut  will  be 


FIG.  80. — Moving  Strut. 


forced  down  and  the  weight  will  move  away  from  the  fixed 
point.  If  the  angle  between  the  strut  and  the  plane  on 
which  the  weight  rests  is  small,  a  comparatively  small  force 
will  move  a  very  heavy  weight.  If  the  angle  be  denoted 
by  a,  the  applied  force  by  P,  and  the  resistance  of  the  weight 
to  being  moved  by  R,  then 

P  X  cos  a  =  R  x  sin  a. 
If  a  be   5°,   cos   a  =  .99619,   sin  a  —  .08716,    and  R  — 


The  resistance  is  not  always  the  weight  of  the  body  to  be 
moved  ;  it  may  be  principally  the  friction  of  the  body  on  the 
plane. 

The  toggle-joint  is  a  combination  of  two  moving  struts. 
It  is  shown  in  Figs.  81  and  82.  It  is  used  where  a  large 
resistance  is  to  be  overcome  through  a  short  distance.  The 
two  struts  have  force  applied  at  their  junction  ;  one  end  of  one 
strut  rests  against  a  fixed  point,  and  the  other  against  the  body 
to  be  moved.  The  force  is  applied  in  a  direction  perpendic- 
ular to  the  direction  of  motion  of  the  body. 

Let  a  be  the  angle  each  strut  makes  with  the  line  joining 


92 


MACHINERY  AND  MECHANICS. 


the  points  about  which  the  outer  ends  of  the  strut  rotate,  P 
the  applied  force,  and  R  the  resistance.      Then 

2R  sin  OL  =  P  cos  a. 

An    example    of    the    toggle-joint    is    found    in     stone- 
crushers. 


FIG.  81, 


FIG.  82. 


WHEEL-WORK,    CRANES,    ETC. 

Fig.  83,  two  wheels  of  unequal  diameters  keyed  to  the 
same  shaft,  illustrates  the  application  of  the  lever  to  wheel- 
work.  That  is,  the  radius  of  one  wheel 
is  the  lever-arm  of  the  applied  force,  and 
the  radius  of  the  other  the  lever-arm  of 
the  weight,  the  pivot  on  which  the  two 
wheels  turn  being  the  fulcrum. 

This  is  the  principle  of  the  wheel- 
work  of  cranes  for  raising  heavy  weights, 
as  used  for  loading  and  unloading  ships, 
handling  ore,  etc.,  in  which  several  pairs 
of  wheels  are  used,  in  connection  with 
each  other,  for  the  purpose  of  making  a 
still  larger  mechanical  advantage,  but 
which  gives  a  corresponding  loss  of  speed.  In  calculating 
such  an  arrangement,  the  wheels  may  be  considered  by  pairs, 
applying  the  law  of  the  lever  in  each  case ;  if  so  desired,  how- 
ever, the  work  may  be  abridged  considerably  by  the  use  of  the 
following  equation,  which  is  deduced  from  the  law  of  the  lever 
and  which  is  known  as  the  Law  of  Wheel-work :  The  continued 
product  of  the  weight  and  the  radii  of  the  wheels  is  equal  to  the 


FIG.  83. 


THE  LEVER  AND  SOME  Oh   ITS  MODIFICATIONS. 


continued  product   of  the  applied  force  and  the  radii  of  the 
pinions. 

If,  in  Fig.  84,  we  let  R,  R^  R2,  ^3,  R^  R5,  R6,  R7,  be  the 
radii  of  the  wheels  A ,  B,  C,  D,  E,  F,  G,  H,  respectively,  then 
P  X  R  X  RZ  X  R,  X  R6  =  W  X  R,  y  R3  X  R,  X  Rr  These 


FIG.  84.— Wheel-work,  Ten   Wheels. 

are  spur-wheels  which  mesh  into  each  other.  The  force  may 
be  applied  at  the  first  wheel  A  by  means  of  a  crank,  or  it  may 
be  turned  by  an  engine,  as  in  the  case  of  the  hoisting-engine. 
Sometimes  the  various  pairs  of  wheels  in  wheel-work  are  con- 
nected by  means  of  belts  or  sprocket-chains  instead  of  teeth. 
In  the  figure  here  shown  the  circles  which  are  tangent  are  the 
pitch-circles  of  the  spur-wheels  which  mesh 
with  -each  other  and  are  so  drawn  to  save  the 
trouble  of  drawing  in  the  teeth. 

The  Block  or  Pulley. — A  pulley-block  in 
a  simple  form  consists  of  two  metal  plates 
carrying  a  grooved  cylindrical  disk  or  sheave. 
The  number  of  sheaves  may  be  increased  and 
the  pulley  is  then  described  as  a  double, 
triple,  etc.,  block.  The  drawing  shows  a 
triple  block  in  perspective.  The  mathemat- 
ical discussion  of  the  pulley  will  be  found  in 
Chapter  I,  page  9. 

The  Differential  Windlass. — This   machine   is  shown   in 
Fig.  S6a  and  consists  of  two  drums  of  unequal  diameter,  D  and 


FIG.  85. 
Triple  Pulley- 
block. 


94 


MACHINERY  AND  MECHANICS. 


d,  upon  the  -opposite  sides  of  which  two  ropes  are  fastened  and 
wound.  By  this  arrangement  the  rope  winds  upon  one  of  the 
drums,  while  it  winds  off  the  other.  A  movable  pulley  hangs 
in  the  loop  of  the  rope,  and  to  this  pulley  is  attached  the 
weight.  The  equation  of  motion  is  derived  from  the  Law 
of  Machines.  The  distance  passed  through  by  the  applied 


W 


FIG.  86«. — Differential  Windlass. 

force  in  one  turn  of  the  crank  is  the  circumference  of  the  circle 
of  which  R  is  the  radius,  that  is,  2  X  3- 1416  X  R.  The  dis- 
tance passed  through  by  the  weight  is 

3.1416  X  D  —  3.1416  X  d 


since  the  rope  is  winding  on  the  large  drum  and  off  the  small 
one,  and  because  the  movable  pulley  will  divide  the  distance 
moved  through  by  the  weight  by  2.  Then,  multiplying  the 
applied  force  and  the  weight  by  the  distances  through  which 
they  move,  respectively,  we  have  the  following  equation  of 
work: 


3-1416 


w 


(3.1416  X  D  —  3.1416  X 


THE  LEVER  AND  SOME  OF  ITS  MODIFICATIONS. 


95 


Dividing  through  by  3. 1416,  we 
have 

FX  2  X  R  = 

for  the  desired  equation. 

The  Differential  Pulley,  or 
differential  hoist,  operates  on  the 
same  principle  as  the  differen- 
tial windlass.  It  consists  of 
two  pulleys  A  and  B,  Fig.  86£, 
keyed  to  the  same  shaft,  and 
which  have  pockets  in  their 
circumferences,  into  which  fit 
the  links  of  a  chain  passing 
around  the  pulleys.  The  chain 
is  endless  and,  in  one  of  its 
loops,  supports  a  single  movable 
pulley,  C.  If  R  be  the  radius 
of  tke  large  pulley  A ,  and  r  the 
radius  of  the  small  pulley 
F  the  applied  force,  and 
weight  to  be  raised,  then 


There  are  other  differential 
hoists,  which  depend  for  their 
action  on  trains  of  gear-wheels, 
which  usually  have  a  sun-and- 
planet  motion.  They  are, 
however,  too  complicated  to  be 
discussed  here. 


DIRECT 
FIG.  86*. 


96  MACHINERY  AND  MECHANICS. 

PROBLEMS. 

i.  In  Fig.  87  let  FM—  4  feet,  FN  '=  12  inches,  and  the  weight 
4000  Ibs.  Find  the  applied  force  in  pounds,  by  the  application  of 
the  law  of  the  lever.  Ans.  1000  Ibs. 

M  F  N 


FIG.   87.  —  Lever. 

2.  In  the  same  figure,  let   the   weight  be  2000  Ibs.,  the  applied 
force  100  Ibs.,  and  FN  4  inches.      How  long  should  FMbe? 

Ans.    6  feet  8  inches. 

3.  In  Fig.  79  let  the  length  of  handle  be  20  inches  and  the  radius  of 
pinion  4  inches,  and  the  force  applied  at  the  end  of  the  handle  200  Ibs. 
What  resistance  will  it  overcome,  neglecting  friction  ? 

Ans.    1000  Ibs. 

4.  In  Fig.  79  let   the  radius  of  the  pinion  be  5  inches,   the  re- 
sistance 600  Ibs.,  and  the  applied  force  100   Ibs.      Find  the  length  of 
the  handle.*  Ans.    2  feet  6  inches. 

5.  If  the  resistance  in  Fig.  79  is  6000  Ibs.,  the  length  of  the  handle 
30  inches,  and  the  radius  of  the  pinion  2  inches,  what  force  at  the  end 
of  the  handle  is  required  to  overcome  it  ?  Ans.   400  Ibs. 

6.  Find  the  radius  of  the  pinion  and  the  length  of  the  handle  of 
a  rack  and  pinion  that  will  raise  a  weight  of  2000  Ibs.  with  an  applied 
force  of  100  Ibs. 

7.  In  Fig.  83  let  the  radius  of  the  larger  wheel  be  20  inches,  and 
the  radius  of  the  small  wheel  4  inches.    What  weight  can  be  raised  with 
an  applied  force  of  100  Ibs.  ?  Ans.    500  Ibs. 

8.  Find  the  diameters  of  two  wheels,  similar  to  those  above,  which 
will  raise  a  weight  of  2000  Ibs.  with  an  applied  force  of  50  Ibs.,  the 
efficiency  being  60  per  cent. 

9.  In  Fig.  84  let  the   radii  of  the  wheels  A,  C,  E,  and  G  be  24 
inches,  20  inches,  16  inches  and  12  inches,  respectively,  and  the  radii 
of  the  pinions  B,  D,  F,  and  H  be  5  inches,  4  inches,  6  inches,   and 
3  inches,  respectively.      Find  what  weight  can   be  raised  with  an  ap- 
plied force  of  100  Ibs.  Ans.   25,600  Ibs. 

*  Friction  is  not  considered  in  Problems  4,  5,  6,  7,  8,  9,  and  10. 


THE  LEVER  AMD  SOME  OF  ITS  MODIFICATIONS.  97 

10.  Design  a  set  of  4  wheels  and  4  pinions  which  will  raise  a 
weight  of  8000  Ibs.  with  an  applied  force  of  100  Ibs. 

Here  we  must  have  100  x  the  product  of  the  radii  of  the  four 
wheels  =  8000  X  the  product  of  the  radii  of  the  four  pinions ;  or, 
letting  P  and  *9  represent  the  above  products,  respectively,  we  have 
the  equation,  100  X  P  =  8000  X  S.  We  may  assume  S  to  be 
3X2X4X2=  48,  that  is,  we  may  assume  that  the  radii  of  the 
pinions  are  3  inches,  4  inches,  2  inches,  and  2  inches,  respectively. 
Substituting  this  in  the  above  equation,  we  have  100^=  8000  X  48 
=  384,000  and  P  =  3840.  The  product  P  of  the  radii  of  the  four 
wheels  must  then  be  3840 ;  that  is,  we  may  make  the  radii  of  the  four 
wheels  of  any  length  so  their  product  is  3840.  These  radii  may  be 
found  by  trial.  10X8x6x8  =  3840.  Therefore  the  radii  of 
the  wheels  may  be  10  inches,  8  inches,  6  inches,  and  8  inches,  respec- 
tively. Where  the  number  of  teeth  on  each  wheel  is  known,  number 
of  teeth  may  be  substituted  for  radius  in  the  above  equation. 

1 1 .  Find  the  diameters  of  the  three  wheels  and  three  pinions  in 
a  crane  which  will  raise  a  weight  of  20,000  Ibs.  with  an  applied  force 
of  200  Ibs.,  the  efficiency  of  the  machine  being  50  per  cent. 

12.  What  weight  can  be  raised  with  an  applied  force  of  100  Ibs. 
with  a  system  of  pulleys  in  which  the  block  contains  three  pulleys  as 
in  Fig.  85,  the  efficiency  being  50  per  cent  ? 

13.  A  weight  of  1800  Ibs.  is  to  be  raised  with  a  system  of  pulleys 
in  which  the  block  contains  3  pulleys.     Find  the  force  necessary,  if 
friction  is  neglected,  to  lift  it. 

14.  A  weight   of  2  tons  is  to  be  raised  with  an  applied  force  of 
500  Ibs.     How  many  pulleys  should  be  put  in  the  block,  friction  be- 
ing neglected? 

15.  What  weight  can  be   raised  with  a  differential  windlass,  the 
large  and  small  drums  being  12  and  8  inches  in  diameter,  respectively; 
the  force  applied  100  Ibs.  and  the  length  of  the  handle  20  inches  ? 

1 6.  What  force  will  be  required  to  raise  a  weight  of  8000  Ibs.  with 
a  differential  windlass,  the  large  and  the  small  drums  being  20  and  12 
inches  in  diameter,  respectively,   and  the  length  of  the   handle  16 
inches  ? 

17.  Design  a  differential  windlass  that  will  raise  a  weight  of  4000 
Ibs.  with  an  applied  force  of  400  Ibs.,  the  length  of  the  handle  being 
20  inches. 


CHAPTER    XII. 
LINK-WORK. 

THE  term  link-work  is  applied  to  such  machinery  as  con- 
sists of  rods,  cranks,  levers,  bars,  etc.,  either  with  parallel 
axes,  intersecting  axes,  or  axes  not  in  the  same  plane.  As 
an  instance,  take  A  and  B,  Fig.  88,  as  fixed  centres  of  motion 


FIG.  88 

AD  as  the  driving  crank,  BE  as  the  driven  crank,  and  DE  as 
the  connecting  rod,  bar,  or  link.  As  AD  turns  about  its 
centre  A ,  the  rod  DE  compels  BE  to  turn  also.  Here  DE  is 
the  link.  When  the  point  C,  where  the  axis  of  the  link  inter- 
sects the  line  of  centres,  is  outside  either  centre,  A  or  £>,  the 
cranks  will  turn  in  the  same  direction,  and  in  opposite  direc- 
tions when  C  is  between  the  centres.  The  connecting-rod  of 
an  engine,  the  pitman  for  giving  motion  to  the  sickle  of  a 
mower,  and  the  valve-rod  of  a  Corliss  engine  are  examples  of 
link-work. 

Link-work  is  the  lightest  running  mechanism  known,  the 
only  resistance  being  due  to  the  slight  friction  made  by  com- 
paratively small  pins  in  well-oiled  bearings.  A  pin  rarely 

98 


LINK-WORK.  99 

makes  more,  and  usually  much  less,  than  one  complete  turn 
in  its  bearing  in  a  complete  movement;  while  in  the  corre- 
sponding movement  with  a  cam  the  roller  (in  the  best  arrange- 
ment) makes  from  6  to  12  or  more  turns  on  its  pin,  and  even 
this  is  not  so  prejudicial  as  regards  resistance  as  the  movement 
of  a  roller  along  the  surface  of  the  cam-groove.  For  the 
above  reason,  link- work  is  much  more  durable  than  other  forms 
of  mechanism ;  hence  it  should  be  adopted,  wherever  possible, 
in  preference  to  toothed  gearing,  cam-work,  belted  gearing, 
etc.  Most  link- work  belongs  to  the  class  in  which  the  axes 
are  parallel,  and  some  examples  will  be  given  in  order  to 
explain  their  action  and  use. 

Fig.    89  is    a   diagram  of   the    Corliss    valve-gear.       The 


FIG.  89. 

wrist-plate  makes  a  partial  rotation  in  order  to  carry  the  pin 
D  back  and  forth  from  H  to  F.  The  valve  and  the  stem  at  B 
are  moved  by  the  link  BE  as  it  swings  from  BE  to  BG. 

As  another  example  *  suppose  that  a  point  is  required  to 
move  from  E  to  F,  Fig.  90,  and  return  within  the  sixth  part 
of  the  revolution  of  the  main  shaft  A,  and  then  allowed  to 
remain  quiet  at  E  for  the  remaining  five  sixths  of  the  turn. 
By  the  use  of  a  cam  this  movement  can  be  easily  made ;  but  if 
there  is  no  particular  objection  to  the  additional  movement  from 
E  to  G  and  return,  link- work  may  be  employed,  as  follows : 
A  is  the  main  shaft,  AD  the  crank,  De  the  pitman,  and 
eBG  =  HBF  a  bell  crank-lever,  the  arrangement  being  such 
that  while  the  crank-pin  moves  from  c  to  b  the  required  sixth 
part  of  the  turn  of  A,  a  moves  to  H  and  back,  and  E  moves 
to  F  and  back,  thus  meeting  the  essential  conditions  of  the 
movement. 

*  Robinson's  "  Principles  of  Mechanism." 


100 


MACHINERY  AND  MECHANICS. 


Paths  of  Various  Points.* — In  the  study  of  link- work  it  is 
often  desirable  to  determine  the  different  simultaneous  positions 
of  each  of  the  joints,  beginning  with  the  driver.  These  positions 

.G 


FIG.  go. 

for  uniform  motion  should  be  equidistant,  as  shown  in  Fig.  91. 
The     crank-pin    D    moves    around    the    circle    12345678 


FIG.  91. 

with  A  as  a  centre.  The  link  BE  moves  about  B  as  a  fixed 
centre  and  about  E  as  a  movable  centre,  E  describing  an  arc 
18273465. 

It  is  required  to  find  the  path  described  by  the  point  F. 

By  an  examination  of  the  figure  it  will  be  seen  that  the 
shortest  distance  between  D  and  F,  and  the  shortest  distance 

*  Robinson's  "  Principles  of  Mechanism." 


LINK-WORK.  101 

between  E  and  F,  will  not  change  for  the  different  simultaneous 
positions. 

Suppose  the  crank  AD  to  be  at  a  point  I  on  the  circle, 
described  by  the  crank;  with  a  radius  equal  to  DE,  and  with 
I,  2,  3,  etc.,  as  centres,  describe  arcs.  Their  intersections  with 
the  arc  18273465  will  be  the  various  positions  of  E. 
Again,  with  DF  as  a  radius,  and  I,  2,  3,  etc.,  of  the  circk- 
12345678,  as  centres,  describe  arcs.  Also  with  I,  2,  3, 
etc.,  of  the  arc  18273465,  as  centres,  and  with  radius  EF, 
describe  other  arcs.  The  corresponding  arcs  intersect  at  1,2, 
3,  etc.,  which  are  required  points  of  the  path  of  F.  Other 
points  may  be  found  in  the  same  manner  and  the  path  more 
fully  determined. 

Equivalents  for  Link-work. — For  every  elementary  com- 
bination in  link-work  the  equivalent  motion  can  be  obtained 
by  wheels  in  rolling  contact,  these  wheels  being  non-circular 
in  form  (see  Fig.  92). 


FIG.  92. 

Dead-points. — One  of  the  objections  to  the  use  of  link-work, 
which  has  to  be  provided  against,  is  what  is  known  as  the 
dead  point. 

A  dead-point  or  a  dead-centre  is  a  point  or  set  of  points  or 
positions  of  the  links  at  which,  if  a  certain  one  of  the  links  in 
•combination  be  made  driver,  the  linkage  will  be  found  locked. 


MACHINERY  AND   MECHANICS. 

often  seen  is  that  of  the  crank  and  connecting-- 
rod of  an  engine.  When  the  crank  and  connecting-rod  are  in 
line  the  crank  cannot  be  started  by  any  amount  of  force  applied 
to  the  cross-head.  It  is  evident  that  in  the  combination  shown 
in  Fig.  93  the  shorter  lever  is  capable  of  turning  completely 


-Dead-point. 

around,  hence  it  is  called  a  crank.  It  is  obviously  possible  for 
the  system  to  come  into  either  of  the  positions  shown  in  Figs. 
93  and  94  in  which  AB  and  BD  coincide.  This  position  in 
which  the  links  coincide  is  called  the  dead-point. 


FIG.  94. — Dead-point. 

Dead-points  are  provided  against  by  special  attachments 
for  the  purpose.  In  the  steam-engine  the  fly-wheel  serves  the 
purpose,  the  momentum  of  the  wheel  carrying  the  crank  over 


LINK-WORK. 


103 


the  dead-centre.  Sometimes  springs  are  used.  In  the  single- 
acting  engine  the  crank  must  not  stop  on  the  dead-centre.  In 
locomotives,  two  sets  of  cranks  are  used,  being  placed  nearly 
at  right  angles  to  each  other,  so  that  while  one  crank  is  on 
the  dead-centre  the  other  is  acting  at  its  best  advantage,  thus 
entirely  obviating  the  liability  of  a  dead-point.  Sometimes 
an  extra  link  is  added,  as  in  Fig. 95,  in  order  to  destroy  the 
dead-point. 


FIG.  95. 

The  examples  and  explanations  thus  far  given  of  link-work 
have  been  of  those  in  which  the  axes  of  the  driver  and  follower 
were  parallel.  Its  use  may  also  be  extended  to  work  in  which 
the  axes  intersect.  This  is  sometimes  called  conical  work  or 
solid  link-work,  the  principal  essential  being  the  bringing  of 
all  the  axial  lines  of  shafts  and  pins  to  a  common  point  O,  as 
in  Fig.  96.  The  use  of  the  conical  link-work  is  similar  to  that 


FIG.  96. — Conical  Link-work. 

of  beveled  and  skew-bevel  wheels  in  that  it  makes  connections 
for  shafts  which  intersect.      Any  of  the  examples  under  axes 


104 


MACHINERY  AND   MECHANICS. 


parallel  may  be  carried  into  conical  link-work,  even  to  the 
extent  of  continued  trains.  As  with  parallel  axes,  every 
elementary  conical  link  combination  may  have  its  equivalent 
in  non-circular  wheels  in  rolling  contact,  and  will  also  be 
subject  to  the  same  conditions  in  regard  to  dead-points. 

A  simple  example  of  this  class  of  link-work  may  be  seen 
in  the  Hooke's  universal  joint,  which  is  employed  as  a  shaft- 
coupling.  The  joint  is  shown  in  Fig.  97,  where  A  and  B  are 


FIG.  97. — Hooke's  Universal  Joint 

the  shafts  to  be  connected,  AD  and  FEE  half  hoops  between 
which  is  a  cross  with  one  branch  at  EF,  parallel  to  the  paper, 
and  the  other  at  D  perpendicular  to  the  paper.  The  branches 
of  the  cross  are  pivoted  at  E  and  F,  and  the  two  points  D  in 
AD*  Sometimes  sliding  parts  are  introduced  into  link-work, 
generally  for  simplifying  the  mechanism,  a  notable  example 
being  that  of  the  cross-head  of  an  engine. 


Robinson's  "  Principles  of  Mechanism." 


CHAPTER    XIII. 


PIPE-FITTINGS. 

Valves. — The  term  ' '  pipe-fittings  ' '  is  used  to  designate  ail 
the  pieces  necessary  for  the  control  of  liquids  and  gases  such  as 
water,  steam,  oil,  ammonia,  etc.,  water  and  steam  being  the 
fluids  most  generally  dealt  with.  These  fittings  are  exclusive 
of  the  piping  itself  and  may  consist  of  valves  and  those  parts  of 
which  the  elbow  and  the  plug  are  examples. 

Valves  may  be  divided  into  the  following  classes : 

(1)  Lifting  Valves;  as  globe-,  gate-,   ball-,  conical-,   and 
some  safety-valves. 

(2)  Rotary  Valves;  as  cocks,  faucets,  throttles,  etc. 

(3)  Hinging  Valves;  as  clack  or  butterfly  check-valves. 

(4)  Spring-valves;  in  which  the  valve 
is  held  on  its  seat  by  means  of  a  strong 
spring,  an  example  of  which  is  the  pop 
safety-valve. 

(5)  Sliding  Valves;  as  the  slide-valve 
on  a  locomotive. 

The  Globe-valve  is  the  most  generally 
used  valve  in  pipe-work,  and  is  used  to 
control  the  passage  of  fluids  through  a 
straight  pipe.  It  generally  consists  of  a 
conical-shaped  disk  which  fits  in  a  simi- 
lar conical-shaped  opening,  the  raising  or 
lowering  of  which  causes  the  passage  to 
be  opened  or  closed.  It  derives  its  name 
from  the  external  appearance,  which  is 

somewhat  globular  in  form.     The  Jenkins  Globe-valve  has  a 

105 


FIG.  98. 
Jenkins  Globe-valve. 


Io6  MACHINERY  AND  MECHANICS. 

flat  disk  and  seat  instead  of  a  conical  one.  The  valve-disk 
contains  a  vulcanized-rubber  ring  which  rests  upon  the  seat 
when  the  valve  is  closed.  This  makes  a  good  valve  because 
the  rubber  makes  a  water-  or  steam-tight  joint.  There  are 
many  valves  which  are  similar  to  the  Globe-valve,  the  differ- 
ence being  that  they  change  the  direction  of  the  passing  fluid ; 
as  the  Angle-valve,  the  Cross-  or  Tee-valve,  and  the  Y-valve. 

The  Gate-  or  Straight-way  Valve. 

By  an  inspection  of  the  sectional  cut  which  is  shown,  of 

the  globe-valve,  it  will  be  noted 
that  the  fluid  in  passing  through 
the  valve  does  not  move  in  a 
straight  line  but  makes  a  turn  of 
almost  a  right  angle.  This  pro- 
duces friction  and  retards  the 
passage  of  the  fluid  to  seme  extent. 
The  gate-valve  shown  in  section 
in  Fig.  99  allows  a  straight 
passage.  For  the  control  of 
water,  this  form  is  especially 
desirable. 

A  Check-valve  is  used  where  it 
is  desired  that  a  fluid  may  pass  in 
one  direction  only  and  be  pre- 
vented from  going  back  by  the 
action  of  the  fluid  itself.  The 
valve  is  automatic,  the  backward 
pressure  of  the  fluid  pushing  the 
valve  against  the  seat  and  the 
forward  pressure  pushing  it  off 
the  seat.  The  check-valve  may 
be  a  lifting-valve,  a  butterfly- 
FIG.  Q9.-Jenkins  Gate-valve.  valve>  or  ball-valve. 

The  Throttle-valve  is  used  on  engines  for  turning  the  steam 


PIPE-FITTINGS.  107 

on  or  off.  The  globe- valve  is  often  used  for  this  purpose, 
but  the  throttle-valve  has  the  advantage  that  it  is  much 
quicker  in  its  action.  This  is  very  desirable  especially  in  case 
of  accident. 


FIG.  100. — Check-valve. 

The  throttle  is  found  on  all  locomotives.  It  may  be  of 
the  rotary  or  sliding  type  of  valves,  or  a  double  poppet-valve, 
shown  at  C,  Fig.  I  50. 

An  example  of  the  Clack-valve  may  be  seen  on  the 
plunger  of  a  suction-pump,  Fig.  202. 

When  a  globe-valve  leaks  it  is  generally  caused  by  the 
wear  of  the  valve-disk  or  the  seat.  This  may  be  remedied  by 
taking  the  valve  apart  and  scraping  the  disk  and  seat  until  a 
good  surface  is  obtained.  With  the  Jenkins  valve  the  leak  can 
generally  be  stopped  by  putting  in  a. new  rubber  disk.  The 
Valve-regrinder  is  a  small  machine  which  is  used  for  reseating 
valves  which  are  worn.  It  is  really  a  small  lathe,  which  fits 
into  the  bonnet  of  the  valve,  with  cutters  that  may  be  adjusted 
to  a  valve  of  any  size.  It  may  be  used  on  the  globe-valve 
with  either  the  conical  or  flat  seat.  This  is  an  invention  which 
makes  a  great  saving,  because  it  makes  possible  the  use  of  old 
valves  which  would  otherwise  have  to  be  thrown  away,  besides 
the  saving  of  time,  it  being  used  on  the  valve  without  taking 
it  from  its  position  on  the  line  of  piping. 


108  MACHINERY  AND  MECHANICS. 

The  Slide-valve  as  used  on  steam-engines  is  shown  in  Fig. 
177. 

The  Poppet-valve,  which  is  also  used  in  engines,  air-com- 
pressors, etc.,  for  the  control  of  operating-fluid  is  shown  in 
Fig.  232. 

For  different  gases  and  acids  it  is  necessary  to  use  valves 
made  of  different  materials ;  for  instance,  a  valve  used  for  the 
control  of  ammonia  in  ice-machinery  is  generally  made  of  iron> 
the  common  brass  valve  being  subject  to  destructive  chemical 
action.  Small  valves  are  generally  made  of  brass,  but  where 
large  piping  is  used  or  where  la"rge  pressures  are  to  be  resisted 
iron-body  valves  are  used. 

The  Back-pressure  valve  is  similar  to  the  check-valve  in 
that  it  allows  a  fluid  to  pass  in  only  one  direction.  It  differs, 
from  the  check-valve,  however,  in  having  its  valve  held 
upon  its  seat  by  means  of  a  lever  and  ball  as  shown  in  Fig. 
101.  With  this  arrangement,  the  fluid  cannot  pass  except  at 


FIG.  101. — Jenkins  Back-pressure  Valve. 

or  above  a  pressure  which  can  be  fixed  at  will  by  moving  the 
weight  further  away  from  or  closer  to  the  pivoted  end  of  the 
lever. 


PIPE-FITTINGS. 


109 


A  section  of  a  reducing-  or  regulating -valve  is  shown  in 
Fig.  102.  This  valve  is  designed 
to  reduce  and  maintain  even  steam- 
pressure,  regardless  of  the  initial 
pressure.  It  will  automatically 
reduce  boiler  or  air-receiver  pres- 
sure in  all  places  when  it  is  desir- 
able to  use  lower  pressure  than 
that  of  the  boiler  or  receiver.  An 
example  of  its  use  may  be  noted 
with  the  steam-accumulator,  Fig. 
210. 

The  following  is  its  mode  of 
operation :  Steam  from  the  boiler 
enters  at  side  "steam-inlet  "  and 
passing  through  the  auxiliary 
valve  K,  which  is  held  open  by 
the  tension  of  the  spring  S,  passes 
down  the  port  marked  ' '  from 
auxiliary  to  cylinder  ' '  underneath 
the  differential  piston  D.  By 
raising  this  piston  D,  the  valve -C 
is  opened  against  the  initial  pres-  FlG- 102.— Mason  Reducing-valve. 
sure,  since  the  area  of  C  is  only  one  half  of  that  of  D.  Steam 
is  thus  admitted  to  the  low-pressure  side,  and  also  passes  up 
the  port  XX  underneath  the  diaphragm  below  S.  When  the 
low  pressure  in  the  system  has  risen  to  a  required  point,  which 
is  determined  by  the  tension  of  the  spring  S,  the  diaphragm 
is  force'd  upward  by  the  steam  in  the  chamber,  the  valve  K 
closes,  and  no  more  steam  is  admitted  under  the  piston  D. 
The  valve  C  is  forced  to  its  seat  by  the  initial  pressure,  thus 
shutting  off  steam  from  the  low-pressure  side.  This  action  is 
repeated  as  long  as  the  low  pressure  drops  below  the  required 
amount.  The  piston  D  is  fitted  with  a  dash-pot  E,  which 
prevents  chattering  or  pounding.  From  the  description  it  is 


no 


MACHINERY  AND  MECHANICS. 


seen  at  once  that  this  is  both  a  reducing-  and  a  regulating- 
valve. 

Piping  is  generally  made  of  wrought  iron,  sometimes  cast 
iron.  In  all  steam-piping  wrought  iron  is  used.  An  example 
of  the  use  of  cast  iron  is  that  of  the  piping  used  in  water- 
mains,  the  different  sections  of  pipe  being  put  together  by 
what  is  known  as  the  ' '  socket-and- spigot ' '  joint,  or  more 
commonly  called  the  bell-joint.  One  end  of  each  section  is 
enlarged  to  a  bell  shape  into  which  fits  the  end  of  the  next 
section,  a  joint  being  made  by  pouring  in  molten  lead  and 
filling  up  the  space  between  the  two  pieces.  With  wrought- 
iron  pipe  the  joint  is  made  by  the  use  of  screw-threads  or 
flanges  and  bolts. 

There  are  two  kinds  of  pipe-fittings  in  use,  those  which  join 
to  the  pipe  by  means  of  screw-threads  and  those  which  join  by 
means  of  flanges.  For  small  work  the  screw-thread  joints  may 
be  used,  but  for  heavy  work  the  flange-joints  are  better. 

Fig.  103  is  an  Elbow  which  is  used  for  making  a  right  angle 
in  a  line  of  piping. 

Fig.  104  represents  a  Tee.  Fig.  105  is  a  Nipple.  Fig. 
1 06  represents  a  Coupling  which  is  used  to  join  the  ends  of  two 


FIG.  103.— Elbow.        FIG.  104.— Tee. 


FIG.  105.— Nipple, 


FIG.  106.— Coupling.  FIG.  107. — Plug.  FIG.  108. — Flange-coupling.* 
pipes.  Fig.  107  shows  the  plug  which  is  used  for  closing  the 
end  of  a  pipe. 

*The  above  cuts  are  furnished  by  the  Lunkenheimer  Company. 


PIPE-FITTINGS.  Ill 

Fig.  1 08  shows  the  Flange-coupling.  A  flange  of  cast  iron 
is  screwed  to  the  end  of  each  of  the  two  pieces  of  pipe  and  the 
flanges  are  then  fastened  together  by  means  of  bolts.  In 
order  to  make  a  tight  joint  a  gasket  made  of  rubber  or  copper 
is  generally  used.  When  the  screw-thread  connection  is  made, 
a  tight  joint  may  be  obtained  by  putting  red  lead  on  the 
threads.  It  should  be  remembered  that  the  examples  given 
above  are  not  meant  to  include  all  the  fittings  used  in  practice 
but  are  mentioned  only  to  give  a  general  idea  of  what  they  are 
like. 

It  should  also  be  remembered  that  any  of  the  above  may 
be  made  with  either  the  screw-thread  or  flange-joint.  For 
instance,  the  elbow  may  be  fastened  to  the  pipes  by  either 
screw-threads  or  flanges.  In  the  latter  case  the  elbow  is  cast 
with  flanges  on  it.  Other  fittings  are  the  Cross,  the  Union,  the 
45°  Elbow,  the  Cap,  the  Right  and  Left  Coupling,  the  Reduc- 
ing Coupling,  the  Retiirn  Bend,  and  others  too  numerous  to 
mention.  When  the  diameter  of  a  pipe  is  spoken  of  the  inside 
diameter  is  meant. 

PROBLEM. 

Devise  a  separator  for  a  steam-engine,  similar  to  that  shown  ii? 
Fig.  200,  of  pipe  fittings.  Draw  a  sketch  of  it  and  write  a  list  of  fre 
fittings  needed.  Let  the  separator  body  be  made  of  6  inch  wrought  - 
iron  pipe  and  the  inlet  and  outlet  of  2-inch  pipe. 


PART  II. 
STEAM-POWER. 


CHAPTER    XIV. 
HEAT  AND  STEAM. 

Heat. — Heat  in  a  substance  results  from  a  motion  of  its  mole- 
cules. The  unit  of  measurement  of  heat  is  the  British  Thermal 
Unit  which  is  the  quantity  of  heat  required  to  raise  the  tempera- 
ture of  one  pound  of  water  one  degree  Fahrenheit.  The  number 
of  heat  units  in  a  pound  of  water  or  steam  at  different  tempera- 
tures is  found  in  Table  I,  in  the  column  headed  "  Total  heat 
in  the  water  above  32°."  Water  at  32°  is  said  to  have  zero  heat 
units. in  it. 

Temperature. — This  term  is  used  as  a  measure  of  the  inten- 
sity of  molecular  vibration.  If  a  certain  number  of  B.T.U.  be 
added  to  one  pound  of  iron,  a  certain  temperature  will  result, 
while  if  the  same  amount  of  heat  be  added  to  two  pounds  of 
iron,  evidently  the  temperature  will  be  less,  even  though  the 
quantity  of  heat  in  both  cases  is  the  same.  Temperature, 
therefore,  is  an  effect  produced  by  heat  but  is  not  a  measure  of 
the  quantity  of  heat. 

Temperature  is  measured  by  noting  the  effect  of  heat  upon 
bodies.  It  is  found  that  heat  will  expand  a  body  and  this 
principle  is  made  use  of  in  thermometers,  pyrometers,  and  other 
instruments  for  measuring  temperatures.  A  thermometer,  in  its 
most  common  form,  consists  of  a  small  glass  tute,  having  a 


HEAT  AND  STEAM.  H3 

very  small  bore  and  a  bulb  at  one  end,  partially  filled  with 
mercury  and  with  graduations  upon  its  entire  length.  Changes 
of  temperature  cause  variations  in  the  height  of  the  mercury, 
by  reason  of  expansion  or  contraction.  In  order  to  arrive  at  a 
standard  method  of  graduation,  two  well-known  facts  are  made 
use  of,  viz.,  that  the  boiling  temperature  of  water  at  atmos- 
pheric pressure  and  the  temperature  of  melting  ice,  are  con- 
stant. In  the  Centigrade  thermometer,  the  freezing  tempera- 
ture is  marked  o°  and  the  boiling  temperature  100°,  while  in  the 
Fahrenheit  thermometer,  the  freezing-point  is  marked  32°,  and 
the  boiling-point  212°.  In  the  former,  that  part  of  the  instru- 
ment between  the  freezing  and  boiling  points  is  divided  into 
100  equal  parts,  while  in  the  Fahrenheit  it  is  divided  into  180 
equal  parts,  each  of  which  is  called  a  degree. 

Absolute  Temperature.— Suppose  that  heat  is  abstracted 
from  a  body  until  it  ceases  to  contract  in  volume.  Its  temper- 
ature is  then  said  to  be  absolute  zero.  It  is  fixed  by  calcula- 
tion and  on  the  Fahrenheit  scale  is  460.70  below  zero. 

Absolute  temperature  on  any  scale  is  the  temperature 
reckoned  from  absolute  zero.  On  the  Fahrenheit  scale  it  is  the 
thermometer  reading  plus  460.70. 

PRESSURE. 

Pressure,  as  applied  to  engineering,  may  be  expressed  (i) 
in  pounds  per  square  inch,  (2)  in  pounds  per  square  foot,  (3) 
in  inches  of  mercury  and  (4)  in  inches  of  water.  Pressure 
expressed  in  either  one  of  these  units,  may  be  reduced  to  the 
equivalent  pressure  in  any  one  of  the  others.  All  the  data 
necessary  for  this  reduction  is  that  (i)  one  cubic  inch  of  mer- 
cury weighs  0.49  pounds  and  (2)  one  cubic  foot  of  water,  at 
60°  F.,  weighs  62.4  pounds.  As  an  example,  a  barometer  read- 
ing of  30  inches  of  mercury  would  correspond  to  a  pressure  of 
30 X. 49  =  14.7  pounds  per  square  inch. 

Atmospheric  or  Barometric  pressure  is  the  pressure  due  to 
the  weight  of  the  atmosphere  and  its  measurement  is  usually 


II4  STEAM-POWER. 

in  inches  of  mercury.     If  no  instrument  for  this  purpose  is 
available,  it  may  be  taken  as  29.92  inches  of  mercury. 

Gauge  pressure  or  pressure  above  atmosphere  is  usually 
measured  by  instruments  which  give  readings  in  pounds  per 
square  inch,  while  pressures  below  the  atmosphere  or  vacuum 
are  usually  measured  by  instruments  which  give  readings  in 
inches  of  mercuiy. 

Absolute  Pressure. — All  laws  concerning  the  pressure,  vol- 
ume, etc.,  of  gases  are  based  upon  a  point  of  absolute  zero 

pressure,  and  since  all  instruments 
for  measuring  pressures  are  from  at- 
mospheric- pressure  up,  it  is  evident 
that  absolute  pressure  must  be  ob- 
tained by  adding  atmospheric  pressure 
to  the  gauge  pressure,  or  if  the  press- 
ure is  below  atmosphere,  reduce  the 
atmospheric  pressure  to  pounds  per 
square  inch  and  subtract  the  given 
pressure  from  it.  These  relations  are 
shown  in  the  accompanying  diagram, 
in  which  a  represents  gauge  pressure;  b,  atmospheric  pressure; 
c9  absolute  pressure;  d,  vacuum;  and  e,  absolute  pressure  in  a 
condenser. 

STEAM. 

If  heat  be  applied  to  one  pound  of  water  at  32°  F.  under  a 
piston  in  a  cylinder,  three  kinds  of  effects  will  be  produced,  viz. : 

(1)  The  temperature   rises  until  the  boiling  temperature  is 
reached,  the  piston  remaining  stationary,  except  for   the  prac- 
tically zero  expansion  of  the  water.     The  boiling  temperature 
varies  with  the  pressure   under  which  the  water  exists  and  is 
shown  in  column  3  of  the  steam  table.     The  number  of  B.T.U. 
which  must  be  added  to  raise  one  pound  of  water  from  32°  to 
the  boiling-point  for  different  pressures  is  found  in  column  4. 

(2)  Further    addition   of    heat,   after    the    boiling-point    is 


HEAT  AND  STEAM.  115 

reached,  does  not  cause  a  corresponding  rise  of  temperature, 
but  steam  begins  to  form  and  the  piston  rises  until  all  the  water 
is  converted  into  steam.  The  water  and  steam  during  this 
phase  remain  at  the  boiling  temperature.  The  heat  added  here 
is  called  the  latent  heat  or  heat  of  vaporization,  and  it  also 
varies  with  the  pressure.  It  is  shown  in  column  6  of  the  steam 
tables.  It  is  found  that  the  volume  under  the  piston  at  the 
end  of  the  vaporizing  process  is  always  a  constant  for  a  given 
pressure.  In  column  8  of  the  steam  table  is  given  the  volume 
of  one  pound  of  steam  at  different  pressures. 

(3)  After  the  water  has  been  entirely  vaporized,  further 
addition  of  heat  causes  a  corresponding  increase  of  the  tem- 
perature and  rise  of  the  piston.  Steam  which  has  thus  received 
heat,  after  complete  vaporization,  is  called  superheated  steam. 

By  adding  the  heat  of  the  water  in  column  4  to  the  corre- 
sponding latent  heat  in  column  6,  we  obtain  the  values  given 
in  column  5,  which  represent  the  total  number  of  heat  units 
required  to  convert  one  pound  of  water  at  32°  into  steam  at  a 
given  pressure. 

Kinds  of  Steam. — If  just  enough  heat  is  added  to  a  pound 
of  water  to  raise  it  to  the  boiling  temperature,  and  then  evap- 
orate all  of  it,  we  have  saturated  steam,  and  the  heat  added  will 
be  H  =  L  +/,  in  which  H  is  total  heat,  L  the  heat  of  vaporiza- 
tion and  /  the  heat  of  the  liquid  or  water. 

If  only  enough  heat  is  added  to  the  pound  of  water  to  raise 
it  from  32°  to  the  boiling-point  and  then  evaporate  only  a 
part  of  it,  we  will  have  steam  containing  some  water  in  suspen- 
sion. This  is  called  wet  steam,  and  the  expression  for  the 
quantity  of  heat  added  will  be,  B.T.U.  added  =  l+xL,  in  which 
x  is  the  weight  of  that  part  of  the  pound  which  has  been  vapor- 
ized. The  temperature  of  the  moisture  in  the  steam  is  the 
same  as  that  of  the  steam. 

If  enough  heat  is  added  to  a  pound  of  water,  to  raise  it 
from  32°  to  the  boiling-point,  to  completely  vaporize  it,  and 
then  to  raise  its  temperature  above  that  corresponding  to  its 


n6  STEAM  POWER. 

pressure,  we  have  superheated,  steam.  An  expression  for  the 
heat  added  is, 

B.T.U.  added=/+L+.53&-0=H+.53(/.-0, 
in  which, 

t8  =  temperature  of  the  superheated  steam  in  de  rees  F. 
t  =  temperature  corresponding  to  the  pressure  as  found  in 

the  steam  tables. 
.53  =  specific  heat  of  superheated  steam. 

Superheated  steam  is  made  by  adding  heat  to  steam  after  it 
has  passed  from  contact  with  the  water  in  the  boiler. 

As  an  example  of  the  use  of  the  steam  tables  in  the  deter- 
mination of  heat  exchange,  let  it  be  required  to  find  the  number 
of  B.T.U.  ne:essary  to  convert  one  pound  of  water  with  a 
temperature  of  80°  F.  into  steam  with  a  pressure  of  100.5 
pounds  absolute  and  containing  2%  moisture 

From  Table  I,  the  heat  in  the  water,  /,  at  80°  F.,  is  48.04. 
The  value  of  I  for  steam  at  100.5  pounds  absolute  is  299.3  anc* 
L  for  the  same  pressure  is  882.7 

The  heat  in  one  pound  of  steam  at  the  given  pressure  is, 
therefore,  299.3 +.98x882.7  =1164.34,  and  the  heat  added  is 
1164.34  —  48  04  =  1116  30.  This  last  subtraction  is  made  because 
the  initial  temperature  of  the  water  was  not  32°,  and  48.04  is 
the  number  of  B.T.U.  already  in  it. 

STEAM  BOILERS. 

Steam  for  use  in  s  eam-engines  is  rrade  in  a  closed  vessel, 
called  a  boiler.  It  is  necessary  that  the  vessel  should  be 
closed  in  order  that  pressure  higher  than  that  of  the  atmosphere 
may  be  obtained.  Steam  may  be  generated  in  an  open  vessel, 
but  it  is  evident  in  this  case  that  the  pressure  of  steam  is  equal 
to  that  of  the  atmosphere.  The  apparatus  for  manufacturing 
steam,  including  the  boiler,  the  furnace,  the  chimney,  the  feed- 
pump, etc.,  is  called  a  steam-boiler  plant.  The  manner  of 
producing  steam  is  as  follows  :  Fuel  is  burned  'in  a  furnace 
which  is  so  situated  with  respect  to  the  boiler  that  the  heat 


HEAT  AND  STEAM.  117 

from  the  burning  fuel  comes  in  contact  with  the  surface  of  the 
boiler,  part  of  the  heat  being  taken  up  by  the  water  in  the 
toiler,  thereby  converting  the  water  into  steam.  The  remain- 
ing heat  is  either  taken  up  the  chimney  by  the  force  of  the 
draft  or  is  lost  by  radiation  from  the  furnace,  boiler,  and  pipes, 
or  by  leakage.  The  office  of  the  furnace  is  to  generate  heat, 
that  of  the  chimney  to  carry  off  the  products  of  combustion 
and  create  a  draft,  and  that  of  the  boiler  to  transfer  heat  into 
the  water,  producing  steam,  and  to  confine  the  steam  under 
pressure. 

CLASSES  OF  BOILERS. 

Steam-boilers  may  be  classed  as  either  Fire-tube  boilers  or 
Water-tube  boilers,  according  to  whether  the  heated  gases  pass 
through  the  tubes  which  are  surrounded  by  water  or  around 
the  tubes  which  contain  water.  These  two  classes  may  be 
further  classed  as  Upright  or  Horizontal,  Marine  or  Land, 
Internally-fired  or  Externally-fired. 

FIRE-TUBE  BOILERS. 

Fig.  109  shows  in  elevation  a  fire-tube  boiler,  known  as  the 
return-tubular  boiler,  and  Fig.  1 10  shows  the  same  in  section. 
The  fuel  is  burned  on  the  grate  in  the  furnace.  The  heated 
gases  rise  and  pass  over  the  bridge-wall  to  the  back  end  of  the 
boiler,  then  return  through  tubes  or  flues  to  the  front  end; 
thence  up  the  chimney  which  is  over  the  front  end  of  the 
furnace.  Part  of  the  heat  of  combustion  is  given  to  the  under 
side  of  the  shell  of  the  boiler,  the  gases  being  somewhat  cooled 
thereby.  A  further  amount  of  heat  is  taken  up  by  the  water 
surrounding  the  tubes,  as  the  hot  gases  pass  through  them. 
Thus  the  heated  gases  are  made  to  remain  in  contact  with  the 
surfaces  which  are  in  contact  with  water  as  long  as  possible  so 
as  to  utilize  a  large  part  of  the  heat.  The  volume  of  the 
boiler-shell  consists  of  two  parts,  the  water-space  and  the 
steam-space.  The  water-space  consists  of  that  part  in  which 
the  water  is  contained.  All  above  this  is  steam-space.  The 


n8 


STEAM  POWER. 


steam-space  shou  d  be  suffic  ently  I.ig  i  to  separ..te  the  parti  Jes 
of  water  carried  up  into  the  sWam  by  th  -  disturbances  caused 
by  boiling.  FOJ  the  purpose  of  providing  for  dry  steam,  the 
steam-dome  is  often  used,  but  it  is  now  often  dispensed  with, 
as  being  unnecessary.  From  the  top  of  the  steam-space  a 


pipe  takes  the  steam  off  to  the  engine,  thus  drawing  off  the 
dryest  steam. 

Heating  Surface. — That  surface  of  the  boiler  which  comes 
in  direct  contact  with  the  heat  f  om  th.1  furnace  is  called  the 


HEAT  AND  STEAM. 


'1 20  5  TEAM-PO  WER. 

"heating  surface."  In  the  return-tubular  boiler  it  consists  of 
the  surface  of  the  shell  in  contact  with  the  hot  gases  (generally 
about  two  thirds  of  the  boiler-shell)  plus  the  inner  surface  of 
the  tubes.  Let  D  =  diameter  of  the  shell  in  feet,  L  the  length 
in  feet,  ;/  the  number  of  tubes,  /  their  length  in  feet,  and  d 
their  diameter  in  inches.  Then  the  heating  surface  of  shell  in 
square  feet  =  3. 1416/2  X  L  X  f ,  the  heating  surface  of  tubes 

3.1416^  X  /  X  n 
in    square    feet  =  -      — .       Total    heating  surface 

•=  f  X  3-  HI6Z2  X  L  +  3'I4l6^2X  /Xn.      The  shell   of  this 

type  of  boiler  is  made  of  steel  or  wrought  iron.  Its  thickness 
is  usually  from  J  to  J  inch.  The  plate  is  put  together  with 
rivets.  One  of  the  greatest  causes  of  trouble  with  this  type  of 
boiler  is  due  to  the  expansion  and  contraction  of  the  tubes, 
which  is  apt  to  cause  leakage  where  the  tube  joins  the  head- 
plate.  Tubes  with  diameters  less  than  6  inches  are  called 
tubes,  while  those  with  diameters  larger  than  6  'inches  are 
generally  called  flues.  The  former  are  fastened  to  the  head- 
plates  by  means  of  tube-expanders,  the  latter  are  riveted 
in.  The  ends  of  the  boiler  above  the  tubes  are  strengthened 
by  tying  them  to  the  side  of  the  boiler  by  means  of  stays  (see 
Fig.  1 10).  This  type  of  boiler  gives  good  results  when  correctly 
proportioned  and  well  managed.  One  objection  to  it  is  that 
it  sometimes  is  the  cause  of  great  loss  of  life  by  explosion,  by 
reason  of  having  the  whole  steam-pressure  in  one  large  vessel. 

The  fire-tube  boiler  may  be  classed  as  either  externally- 
fired  or  internally-fired.  The  externally-fired  boiler  has 
already  been  described. 

Internally-fired  Boilers. — The  internally-fired  boiler  has 
its  furnace  within  the  shell  in  a  flue  which  is  made  large  enough 
to  contain  a  grate.  The  gases  may  pass  to  the  back  in  this 
flue  and  then  return  to  the  front  in  small  tubes  above  the  fire- 
flue  as  in  the  case  of  the  return-tubular  boiler,  or  they  may 
pass  to  the  back  and  then  to  the  front  through  openings  in 
the  brick  setting  and  then  to  the  back  again  and  out  the  chim- 


HEAT  AND  STEAM. 


121 


ney  by  another  passage  under  the  shell.  The  latter  plan  is- 
illustrated  by  Fig.  ill,  showing  the  Cornish  boiler,  one  of  the 
earlier  forms  of  boiler,  of  English  origin. 

An  example  of  the  former  is  shown  in  the  Cylindrical 
Marine,  or  Scotch,  boiler,  Fig.  112,  in  which  the  combustion 
takes  place  in  two  large  flues,  passes  to  the  <4back  connec- 
tion ' '  and  then  to  the  front  through  small  tubes  above  the 


FIG.  in. — Cornish  Boiler. 

flues  and  up  the  stack.  The  Locomotive  boiler,  Fig.  113,*  is 
an  internally-fired  boiler,  in  which  the  heated  gases  of  combus- 
tion pass  directly  from  the  front  to  the  rear  of  the  boiler  through 
fire-tubes  and  then  out  through  the  back  connection  and  the 
smoke-stack.  The  fire-box  is  of  a  rectangular  form  as  shown 
in  cut. 

Water-tube  Boilers. — As  before  stated,  the  water-tube 
boiler  has  its  tubes  filled  with  water,  and  surrounded  by  hot 
gases.  Fig.  1 14  shows  a  side  view  of  the  Babcock  &  Wilcox 
boiler,  which  is  an  example  of  this  type.  The  boiler  is  made  up 
of  a  number  of  vertical  sections,  standing  side  by  side.  Each 
section  consists  of  several  tubes  connected  one  above  the  other, 
at  each  end  to  a  header,  the  headers  being  connected  at  the 
top  to  a  large  steam-  and  water-drum.  Fig.  115  shows  one 

*  Figs.  109,  no,  112,  113  are  furnished  by  Messrs.  E.  Hodge  &  Co. 


122 


STEAM-POWER. 


\        4-20" 


FIG.  112. — Scotch  Boiler. 


HEAT  AND  STEAM. 

^ 


123 


124 


STEAM-POWER. 


of  these  headers.  It  is  made  of  cast  iron  or  wrought  steel. 
The  tubes  are  placed  over  each  other  in  zigzag  fashion  in  order 
to  intercept  as  much  as  possible  the  gaseous  currents.  The 
tubes  are  made  of  wrought  iron  or  steel,  and  are  fastened  to 


FIG.  114. — Babcock  and  Wilcox  Boiler.* 


FIG  115. — Babcock  and  Wilcox  Header.* 

the  header  by  means  of  a  tube-expander.  Fig.  116  shows  a 
portion  of  the  end  of  a  tube  and  a  header  in  section  showing 
the  arrangement  for  getting  at  the  end  of  the  tubes  for  the 
purpose  of  inspection  and  cleaning.  By  taking  off  the  hand- 
hole  nut  the  hand-hole  cover  may  be  taken  off  and  an  opening 
made  in  the  header-wall  opposite  the  wall  entered  by  the  tube. 
The  same  figure  shows  how  the  feed-water  enters  near  the  bottom, 
of  the  drum.  The  tubes  slant  downwards  toward  the  back  in 
order  to  facilitate  the  circulation  of  the  water.  The  heated 
water  tends  to  rise  and  the  water  in  the  drum  above  flows  down 
through  the  rear  headers  to  take  its  place.  A  mud-drum  is. 

*  From  "  Steam,"  by  permission  of  the  Babcock  and  Wilcox  Co. 


HEAT  AND   STEAM. 


125 


connected  to  the  lower  end  of  the  rear  headers,  as  shown  in 
the  side  elevation,  Fig.  114.  Sometimes  the  tubes  are  all 
fastened  to  one  header  at  each  end  as  in  the  Heine  boiler, 


Fig.  117.      The  boiler,  however,  made  up  of  sections,  has  the 
advantage  of  being  more  easily  handled. 

Another   type  of  the  water-tube   boiler   is   shown   in   the 
Stirling  boiler,  Fig.  118,  which  consists  of  three  large  drums 


126  STEAM-POWER. 

connected  to  a  fourth  drum  below  them  by  means  of  nearly 
vertical  small  tubes.  The  hot  gases  come  in  contact  with 
these  small  tubes  and  part  of  the  drum-surface,  being  made  to 
pass  in  contact  at  the  proper  time  and  in  the  proper  direction 
by  means  of  deflecting-plates,  as  shown  in  the  figure. 

Water-tube  boilers  are  ' '  quick  steamers  ' '  because  of  the 
small  volume  of  water  in  each  tube,  each  tube  also  being  sur- 
rounded almost  entirely  by  hot  gases.  They  have  an  advan- 
tage also  in  that  the  pressure  is  confined  mainly  in  small  tubes. 


FIG.  117. — Heine  Boiler. 

This  makes  the  resistance  to  rupture  much  more  perfect,  and 
for  this  reason  many  makers  of  water-tube  boilers  call  their 
boilers  "safety-boilers."  The  heating  surface  of  water-tube 
boilers  consists  of  the  outside  surface  of  the  tubes,  headers, 
etc.,  in  contact  with  hot  gases. 

BOILER-SETTING. 

By  the  term  setting  is  meant  the  general  arrangement  of 
the  boiler,  furnace,  and  chimney  with  regard  to  each  other  and 
the  manner  of  closing  the  boiler  in.  By  an  inspection  of  the 


HEAT   AND  STEAM. 


127 


FIG.  118.— Stirling  Boiler. 


128 


STEAM-POWER. 


different  forms  and  shapes  of  the  boilers  already  described  it  is 
readily  seen  that  the  setting  will  depend  largely  upon  the  make 
of  the  boiler.  Fig.  119  and  Fig.  120  show  two  views  of  the 


FIG.  119. — Boiler-setting. 

+> 

"  setting  "  for  a  return-tubular  boiler.  The  walls  of  the  fur- 
nace are  sometimes  "  battered,"  that  is,  the  inner  surface  of 
the  walls  is  inclined  outward  from  the  vertical.  This  enlarges 
the  combustion-chamber. 

The  line  along  the  side  of  the  boiler  at  which  the  brick- 
work joins  the  shell  is  called  the  fire-line.  This  determines 
the  amount  of  shell-surface  in  direct  contact  with  the  heat.  It 
is  generally  about  two  thirds  of  the  boiler-surface.  The  walls 
should  be  thick  enough  to  prevent  radiation.  It  is  best  to 
have  a  double  wall  with  an  air-space  between.  This  prevents 
cracking  and  consequent  leakage  of  heat  of  the  walls  due  to 
unequal  expansion.  This  double  wall  is  equally  important 
where  there  are  several  boilers  side  by  side  (called  a  battery^. 

The  grate-surface  is  made  up  of  a  number  of  grate-bars 
placed  side  by  side.  The  grate-bar  is  seldom  longer  than 
4  feet.  The  total  length  of  grate  is  seldom  more  than  7  feet. 
For  this  case  it  is  necessary  to  have  two  lengths  of  grate-bars 
placed  end  to  end  and  supported  at  the  middle.  The  grate 


HE  A  T  AND  STEAM. 


129 


rests  on  the  dead -plate  at  the  front  and  on  the  bridge-wall  at 
the  back  end.  The  grate  is  inclined  slightly  from  the  front 
toward  the  back  end,  usually  about  f  inch  fall  for  every  foot 
of  length  of  grate. 

The  bridge-wall  rises   from   the   back   end  of  the   grate, 
making  an  -angle  of  about  45°  with  the  horizontal.     The  object 


FIG.  120. — Boiler-setting. 

of  this  is  to  deflect  the  furnace  flames  in  such  a  manner  as  to 
spread  them  and  cause  them  to  follow  along  the  under  surface 
of  the  boiler.  On  this  account  the  hottest  part  of  the  boiler- 
furnace  is  just  behind  the  bridge-wall.  Sometimes  the  top  of 
the  bridge-wall  is  a  straight  horizontal  line  as  in  Fig.  120. 
In  other  cases  it  is  curved  to  conform  to  the  shape  of  the 
boiler. 

The  ash-pit  is  the  space  between  the  grate  and  the  bottom 
of  the  furnace.  It  is  formed  by  the  sides  of  the  furnace  and 
paved  at  the  bottom,  usually  in  order  that  water  may  lie  in  it. 

The  flame-bed  is  that  part  of  the  furnace  just  back  of  the 
bridge-wall  and  extending  to  the  back  end  of  the  furnace.  It 
inclines  downward  from  near  the  top  of  the  bridge-wall  to  the 


'30 


STEAM-POWER. 


level  of  the  boiler-room  floor.  This  inclination  causes  the  soot 
and  ashes  drawn  over  the  bridge-wall  by  the  force  of  the  draft 
to  fall  towards  the  back.  In  this  way  the  cleaning  is  facilitated. 
A  cleaning-door  is  made  in  the  back  wall  through  which 
ashes,  etc.,  are  taken  out.  The  boiler  is  set  a  trifle  lower  at 
the  back  end  than  at  the  front  end.  This  is  done  in  order  to 
drain  the  boiler  toward  the  blow-off  pipe. 

Hanging  the  Boiler. — Supporting  the  heavy  weight  of  the 
boiler  itself  and  its  volume  of  water  is  effected  in  two  ways : 
The  boiler  is  supported  at  its  sides  by  the  furnace- walls,  .or  it 
is  hung  from  beams  above  by  means  of  links  and  eyes  attached 
to  its  upper  part.  The  first  plan  is  carried  out  by  riveting 
"brackets  "  of  steel  or  cast  iron,  at  least  two  to  each  side,  to 
the  boiler  as  in  Fig.  109.  These  brackets  rest  on  a  place 
made  for  them  on  the  walls.  The  walls  of  the  furnace  are  apt 
to  be  spread  apart  by  reason  of  the  expansion  of  the  boiler 
when  heated,  if  the  bracket  is  fixed  movably  on  the  wall. 

Rollers  are  sometimes  put  between  the  bracket  and  its  seat 
for  the  purpose  of  avoiding  this  trouble.  Fig.  12 1  shows  an 


FIG.  121. — Eye  Riveted  to  Boiler-shell. 

eye  riveted  to  the  boiler-shell,  into  which  is  fitted  a  hooked  link 
for  supporting  the  boiler  from  above.  Owing  to  the  different 
forms  and  dimensions  of  water-tube  boilers,  no  established  rule 


HEAT  AND  STEAM.  131 

can  be  adopted  for  setting  them.  Each 
make  has  its  own  special  setting,  which  is 
usually  specified  by  the  maker.  Fig.  1 14 
shows  the  setting  of  the  Babcock  &  Wilcox 
boiler,  and  Fig.  1 1 8  the  setting  of  the  Stirl- 
ing boiler. 


CHIMNEYS. 

The  connection  of  the  chimney  to  the 
setting  will  depend  upon  the  type  of  the 
boiler.  For  the  return-tubular  boiler  shown 
in  Figs.  109  and  1 10,  the  stack  connects 
with  the  front  end.  For  the  locomotive 
boiler  it  is  on  the  end  of  the  boiler  opposite 
the  furnace.  With  most  water-tube  boilers 
the  stack  is  at  the  back  end. 

The  material  used  in  building  stacks  is 
usually  either  steel,  wrought  iron,  or  brick. 
The  brick  chimney  is  of  much  greater  first 
cost  and  it  is  apt  to  leak  by  reason  of 
cracks.  Its  great  weight  makes  the  con- 
struction of  the  foundation  a  serious  problem. 
The  brick  chimney  is  usually  made  with 
double  walls  with  an  air-space  between. 
The  outer  wall  is  thick,  and  of  ordinary  brick, 
giving  stability  to  the  structure,  while  the 
inner  wall  is  thin  and  made  of  fire-brick  (see 
Fig.  122). 

Steel  or  wrought-iron  chimneys  are  made 
of  sections  riveted  together.      They  may  be" 
made  practically  air-tight.      The  higher  the 
chimney  the  greater  the  force  of  the  draft. , 
The  air  on  the  inside  of  the  chimney,  being 
heated,   expands  and    becomes    lighter  and 
therefore    lower    in    pressure    than    the    air. 


- 


I3  2 


STEAM-POWER. 


on  the  outside,  hence  the  temperature  of  the  gases  entering 
the  bottom  of  the  chimney  affect  the  draft  force.  The  force 
of  the  draft  is  equivalent  to  the  difference  in  weight  of  the 
column  of  heated  gases  inside  of  the  chimney  and  that  of  an 
equal  column  of  the  outside  air.  The  draft  is  usually  spoken 
of  as  "  so  many  inches  of  water.  "  It  is  determined  by  means 
of  the  U-tube  gauge  shown  in  Fig.  123. 


FIG.  123.— U-tube  Draft-gauge. 

One  end  is  connected  by  a  rubber  connection  or  otherwise 
to  the  inside  of  the  stack  near  the  base,  the  other  end  being 
open  to  the  atmosphere.  The  difference  in  level  in  the  two 
legs  measures  the  draft  in  inches  of  water  =  h  in  the  figure. 
It  usually  ranges  from  i  to  J  inch. 

The  following  formulas  for  dimensions  of  chimneys  are 
given  by  Kent: 

H.P.  =  3.33£y77=  3.33(^4  -  0.6  VA}  VH. 


0.3 


HEAT  AND  STEAM.  133 

For  round  chimneys,  diameter  of  chimney  =  diameter  of 
E  +  4  inches. 

For  square  chimneys  side  of  chimney  in  feet  =  V£  -f-  4 
inches. 

In  these  formulas  H.P.  =  commercial  horse-power  of 
boiler,  I  H.P.  taken  as  equivalent  to  5  Ibs.  of  coal  burned  per 
hour;  A  =  area  of  chimney  and  E  =  effective  area  in  square 
feet.  H=  height  in  feet. 

It  is  usual  in  chimney  design  to  assume  the  height  of  the 
chimney  such  that  the  smoke,  etc.,  is  carried  above  the  sur- 
rounding buildings  and  then  find  the  corresponding  area  by 
means  of  the  formula. 

The  passage  which  connects  the  different  boilers  of  a 
battery  to  the  main  chimney  is  called  the  ' '  breeching. ' '  It 
is  generally  made  of  sheet  iron. 

Forced  Draft  is  the  term  used  in  designating  all  means  of 
draft  production  other  than  that  of  the  chimney.  In  the  loco- 
motive forced  draft  is  produced  by  passing  the  exhaust  steam 
through  the  stack  in  such  a  manner  that  a  current  of  air  is 
induced  through  the  furnace.  This  method  is  also  frequently 
adopted  in  stationary  practice,  but  it  has  the  objectionable 
features  of  making  a  disagreeable  noise,  especially  in  an  iron 
stack,  and  of  rusting  the  metal  parts  due  to  the  moisture  in 
the  steam.  It  is  also  wasteful  of  steam,  on  account  of  its 
causing  back-pressure  on  the  engine. 

The  most  common  method  of  producing  a  forced  draft  is 
to  produce  a  current  through  the  furnace  and  stack  by  means 
of  a  fan  or  blower,  which  is  usually  run  by  a  small  indepen- 
dent engine.  Here  the  force  of  the  draft  may  be  controlled 
by  the  speed  of  the  engine.  Fig.  1 24  shows  an  arrangement 
for  producing  induced  draft.  The  fan  is  placed  at  the  back 
end  of  the  boiler.  The  fan  consists  of  a  number  of  vanes  on 
a  revolving  shaft.  It  revolves  within  an  iron  casing.  The 
small  engine  which  runs  it  is  shown  at  the  right  of  the  cut. 
Fig.  125  shows  another  method  of  producing  draft  in  which  the 
grate  is  made  up  of  hollow  pipes. 


134 


STEAM-POWER. 


The  pipes  are  perforated  and  air  is  forced  through  them 
and  the  fuel  by  means  of  a  blower.      By  having  forced  draft 


FIG.  124.— Sturtevant  Blower  Plant. 


the  chimney  or  stack  needs  only  to  be  high  enough  to  carry 
the  smoke  above  the  surrounding  buildings. 


HEAT  AND  STEAM. 


'35 


FUELS   AND    COMBUSTION. 

Combustion  is  rapid  oxidation  accompanied  with  heat  and 
light. 

The  Rate  of  Combustion  is  measured  by  the  number  of  pounds 
of  fuel  burned  on  one  square  foot  of  grate-surface  in  one  hour. 
It  depends  mainly  upon  the  nature  of  the  fuel  and  the  force  of 
draft.  A  maximum  rate  is  generally  produced  when  forced 


FIG.   125. — Forced-draft  Fan. 

draft  is  used  with  an  inferior  fuel,  while  the  minimum  rate  is 
produced  with  natural  draft  and  the  best  grades  of  fuel. 

In  locomotive  practice  a  rate  of  combustion  as  high  as 
200  Ibs.  of  coal  per  square  foot  of  grate  per  hour  is  sometimes 
used.  The  ordinary  rate  for  stationary  boilers  generally 
ranges  between  10  and  25  Ibs.,  and  as  low  as  3  or  4  Ibs.  is 
sometimes  found  in  small  boilers  used  for  steam-heating. 

The  principal  elements  in  fuels  are  Hydrogen,  Carbonr 
and  Oxygen.  Carbon  may  combine  with  oxygen  and  form 
two  different  chemical  compounds,  carbon  monoxide,  CO, 
and  carbon  dioxide,  CO2;  that  is,  one  atom  of  carbon  and  one 
of  oxygen  or  one  atom  of  carbon  with  two  of  oxygen.  The 
former  is  produced  by  limiting  the  supply  of  air  and  the  latter 
by  an  abundant  air-supply.  When  it  burns  to  CO2  or  carbon 


136  STEAM-POWER. 

dioxide,  14,600  heat-units  are  produced  per  pound  of  carbon 
When  it  burns  to  CO  or  carbon  monoxide,  4450  heat-units  per 
pound  of  carbon  are  produced.  Hence  10,150  heat-units  per 
pound  of  fuel  are  lost  by  improperly  ventilating  the  fuel  during 
combustion. 

Hydrogen  combines  with  oxygen  in  the  proportion  of  I  Ib. 
of  hydrogen  to  8  Ibs.  of  oxygen,  or  2  atoms  of  hydrogen  to  I 
of  oxygen.  In  so  doing  a  pound  of  hydrogen  gives  up  62,000 
heat-units.  The  oxygen  in  the  fuel  does  not  burn,  but  will 
neutralize  one  eighth  of  its  weight  of  hydrogen.  Then  if 
•C,  H,  and  O,  represent  the  proportions  of  carbon,  hydrogenf 
and  oxygen  in  the  pound  of  fuel,  the  number  of  heat-units, 


h  =  J4,6ooC  +  62,oooH  -....     (i) 

The  proportion  of  different  elements  in  a  pound  of  fuel  is 
determined  by  chemical  analysis.  Owing  to  the  different 
wastes  of  heat  by  radiation,  by  dropping  of  fuel  through  the 
grate,  by  incomplete  combustion,  and  by  the  hot  gases  escap- 
ing through  the  chimney,  much  of  this  heat  is  not  taken  up  in 
producing  steam.  The  amount  utilized  may  range  from  50  to 
75  per  cent  of  the  total  heat,  depending  upon  the  excellence 
of  design,  and  upon  the  conditions  of  operation. 

The  total  heat  required  to  be  generated  in  the  furnace  is 
calculated  by  first  finding  the  weight  of  steam  required  per 
hour  to  run  the  engines  or  other  apparatus.  By  the  use  of  the 
steam-table  the  number  of  heat-units  required  to  produce  this 
weight  of  steam  is  found  as  follows  :  Let  H  =  the  total  heat 
above  32°  of  I  Ib.  of  steam,  as  taken  from  the  steam-table  for 
the  given  pressure,  and  let  /  be  the  heat  in  the  water  for  the 
given  feed-water  temperature;  then  H  —  I  is  the  heat  required 
to  evaporate  i  Ib.  of  water  from  the  given  feed-water  tempera- 
ture into  steam  of  the  given  pressure. 

If  K  =  the  number  of  heat-units  that  may  be  generated  by 
the  complete  combustion  of  i  Ib.  of  the  coal  which  is  to  be 
used,  and  E  the  efficiency  of  the  boiler  which  may  be  expected 


HEAT  AND  SJEAM. 


37 


under  running  conditions  (say  from  0.5  too./)  then 


H-  I 
EK 


the  quantity  of  coal  required  to  generate  each  pound  of  steam. 

Air  Required  for  Combustion. 

The  quantity  of  air  supplied  to  the  furnace  should  be  more 
than  the  quantity  actually  necessary  for  the  combustion  of  the 
fuel.  It  is  necessary  to  supply  not  less  than  about  18  Ibs.  of 
air  to  the  furnace  for  every  pound  of  carbon  in  the  coal  in  order 
to  obtain  complete  combustion. 

Fuels . 

The  principal  fuels  used  in  boiler-furnaces  are  wood,  coal, 
and  petroleum.  Wood  and  coal  are  burned  on  the  ordinary 
grate.  Petroleum  requires  a  special  apparatus  for  feeding 
which  will  be  described  later.  Coal  is  used  more  than  any 
other  fuel.  Wood  is  mostly  used  where  local  conditions  call 
for  it,  as  in  a  sawmill  plant,  or  in  a  wooded  locality.  Wood 
burns  with  a  bright  flame  and  rapidly.  Its  percentage  of 
carbon  is  comparatively  small  and  that  of  the  volatile  gases 
large. 

Coal  may  be  divided  into  two  great  classes :  Anthracite  or 
hard  coal  and  Bituminous  or  soft  coal.  Anthracite  burns 
slowly  with  little  flame.  Its  percentage  of  carbon  is  large  and 
hence  it  is  a  great  producer  of  heat.  The  percentage  of 
volatile  gases  is  small.  Bituminous  coal  breaks  easily,  burns 
more  rapidly,  and  with  more  flame  than  the  anthracite.  Its 
percentage  of  volatile  matter  is  from  20  to  50. 

A  better  classification  is  the  following,  taken  from  Kent's 
"  Steam-boiler  Economy. ' ' 


Fixed 
Carbon 
Per  cent. 
(In  the  Co 

Volatile 
matter. 
Per  cent, 
mbustible.) 

Heating  Value 
per  Ib. 
Combustible. 

Relative  Value 
of  the 
Combustible. 
Semi-hr.  =  100. 

Anthracite    

Q7  tO  Q2   5 

3  tO      7   ^ 

14  600  to  14  800 

Q-2 

Q2  ?    "  87  c 

7  e    "   TO   C 

14  700       15  ooo 

VJ 
OJ. 

Semi-bituminous  
Bituminous,  Eastern.. 
Western. 
Lignite  

87.5   "  75 
75  "  60 
65  "  50 
under  50 

'2.5  "  25 

25    "  40 

35  "  50 

15,500      16,000 
14,800       15,200 
13,500      14,800 

1  1  OOO         I"?  5OO 

100 

95 
90 

11 

11 

138  STEAM-POWER. 

The  anthracite  and  semi-anthracite  coals  are  found  in 
eastern  Pennsylvania;  the  semi-bituminous  in  a  very  narrow 
stretch  of  territory  from  central  Pennsylvania  to  the  southern 
boundary  of  Virginia;  the  eastern  bituminous  coals  in  the 
remainder  of  the  Appalachian  coal-field  from  northern  Penn- 
sylvania and  Ohio  to  Alabama.  The  western  bituminous  coals 
and  the  lignites  are  found  west  of  the  State  of  Ohio.  They 
are  characterized  by  being  high  in  moisture  as  well  as  in 
volatile  matter. 

The  figures  in  the  above  table  refer  to  the  combustible 
portion  of  the  coal,  that  is,  the  carbon  and  the  volatile  matter, 
not  including  the  ash  and  the  moisture.  The  percentage  of 
ash  varies  greatly  in  all  the  several  classes.  It  may  be  as  low 
as  5  per  cent  and  as  high  as  30  per  cent. 

Coke  is  made  from  bituminous  coal  in  a  manner  corre- 
sponding to  that  of  producing  charcoal  from  wood.  It  pro- 
duces little  smoke  and  is  an  efficient  heat-giving  fuel. 

Petroleum  has  a  heating  value  of  about  50  per  cent  greater 
than  average  good  coal  per  pound.  It  is  burned  with  less 
cost  of  labor  in  feeding  it. 

Firing. — The  term  firing  is  used  to  designate  the  process 
of  burning  the  fuel  on  the  grate.  It  consists  of  keeping  the 
fire  in  a  clean  condition,  regulating  the  draft-supply,  etc. 
There  are  systems  of  firing,  among  which  is  the  spreading 
system,  in  which  the  fuel  is  spread  all  over  the  grate-area  in 
thin  layers  at  frequent  intervals  of  time.  Thick  layers  always 
choke  the  draft  and  consequently  cool  the  furnace. 

The  alternating  system  requires  a  wide  grate.  A  charge 
is  first  put  on  one  side  and  allowed  to  burn  a  while,  when 
another  charge  is  placed  on  the  other  side.  This  keeps  one 
side  of  the  furnace  hot  all  the  time  and  the  volatile  gases  from 
the  new  charge  pass  over  the  hot  part  of  the  furnace  and  are 
burned. 

The  coking  system  consists  of  placing  the  charge  upon  the 
dead-plate  in  front  of  the  grate  and  gradually  pushing  it  back 
toward  the  bridge-wall.  This  makes  the  hottest  part  of  the 


HE  A  T  AND  STEAM  139 

furnace  toward  the  back,  and  the  volatile  gases,  being  driven 
off  soon  after  the  charge  is  placed  in  the  front  of  the  furnace, 
pass  over  this  heated  part  at  the  back  and  are  burned.  This 
process  of  firing  is  usually  carried  out  by  means  of  a  mechanical 
arrangement  called  a  Mechanical  Stoker.  The  fuel  is  placed 
in  a  hopper  and  is  taken  thence  to  a  moving  grate,  either  end- 
less or  reciprocating,  which  causes  the  fuel  to  move  gradually 
to  the  back  end,  burning  in  the  meantime.  Fig.  126  shows 
the  Roney  stoker.  The  crank-disk  which  receives  its  motion 
direct  from  the  engine  gives  motion  to  the  whole  stoker.  The 
coal  is  placed  in  the  hopper.  It  is  pushed  over  the  dead-plate 
to  the  grate-bars  by  means  of  the  pusher  and  the  feed-plate. 
The  grate  consists  of  bars  arranged  in  steps  which  take  an 
inclined  and  then  a  stepped  position,  which  causes  a  movement 
of  the  fuel  toward  the  back  end.  Motion  is  transmitted  to  the 
grate-bars  through  the  connecting-rod  and  rocker-bar.  The 
quantity  of  fuel  fed  out  of  the  hopper  is  regulated  by  the  feed- 
wheel. 

Petroleum  Fuel. — The  usual  method  is  to  supply  the  oil 
to  the  furnace  in  the  shape  of  finely  divided  particles,  which 
are  forced  into  the  furnace  by  a  steam-  or  air-injector.  Steam 
or  compressed  air  is  made  to  pass  through  annular  openings 
drawing  the  oil  up.  This  makes  a  finely  divided  mixture  of 
air  and  oil,  or  steam  and  oil,  which  is  sprayed  into  the  ordinary 
furnace  and  burned.  Using  steam  for  this  purpose  has  the 
advantage  of  being  the  cheaper  arrangement,  but  it  has  the 
objectionable  feature  of  introducing  moisture  from  the  steam 
into  the  furnace.  When  compressed  air  is  used  an  air-com- 
pressor supplies  air  to  a  large  reservoir,  which  holds  the  air 
necessary  to  start  again  after  the  steam-pressure  in  the  boiler 
is  down.  Fig.  127  shows  the  arrangement  of  a  plant  for 
burning  petroleum  by  means  of  compressed  air.  Fig.  128  is 
a  sectional  view  of  an  oil-feeder. 


140 


STEAM-POWER. 


HEAT  AND  STEAM. 


141 


*Fic.  127. — Plant  for  Burning  Petroleum  Fuel.  /=  oil-tank;  /=  pipe 
leading  from  /  to  the  burner  A  ;  GG  =  air-compressor  which  keeps 
a  supply  of  air  in  the  tank  just  by  its  side. 


*  FIG.  128.— Section  of  Burner.  C  —  air-entrance  ;  B  =  oil-entrance  ; 
F  =  air-valve  ;  A  =  pipe  leading  to  combustion-chamber  under 
boiler. 

*  From  "  A  Treatise  on  Fuel,"  by  Arthur  V.  Abbott. 


142 


STEAM-POWER. 


BOILER    ACCESSORIES. 

The  articles  named  and  described  under  this  head  are 
usually  necessary  for  any  boiler  no  matter  what  the  make  or 
type. 

Steam-gauge. — This  is  an  instrument  connected  by  a  small 
pipe  to  the  steam-space  of  the  boiler  for  indicating  at  a  glance 
the  condition  of  the  steam-pressure  in  the  boiler.  Fig.  129 


FIG.  129. — Ashcroft  Steam-gauge. 

shows  the  internal  mechanism  of  a  steam-pressure  gauge. 
The  steam- pressure  enters  it  at  the  bottom  and  enters  the  flat 
curved  tube,  which  is  connected  at  one  end  to  the  needle. 
When  the  pressure  is  increased  the  ends  of  the  spring  spread 
apart  and  the  needle  is  turned  around  the  dial  accordingly. 

The  Water-gauge. — This  consists  of  a  glass  tube,  generally 
about  1 2  inches  long,  one  end  of  which  is  on  a  level  with  the 
water-space  and  the  other  on  a  level  with  the  steam-space. 


HEAT  AND  STEAM. 


143 


The  water  always  stands  at  the  same  level  in  the  glass  as  in 
the  boiler,  and  the  gauge  thus  shows  at  a  glance  the  height  of 
the  water  in  the  boiler.  For  the  same  purpose  gauge-cocks, 
generally  three,  are  placed  in  connection  with  the  boiler,  one 
with  the  steam-space,  one  with  the  water-space,  and  one  at 
about  the  level  of  the  water-line.  By  opening  these  the  height 
of  the  water  may  be  determined.  They  are  used  for  the  pur- 
pose of  having  a  reliable  source  of  information  even  if  the 
gauge-glass  should  get  out  of  order. 

The  Water-column. — The  gauge-glass,  pressure-gauge, 
and  gauge-cocks  are  all  usually  connected 
to  the  water-column  as  shown  in  Fig. 
130.  The  water-column  is  usually  made 
of  cast  iron.  In  order  to  keep  the  tube 
in  the  gauge,  to  which  the  needle  is 
attached,  from  becoming  too  hot  and 
thus  making  an  inaccurate  reading,  water 
is  kept  in  it  by  means  of  a  loop  in  the 
pipe-connection  of  the  gauge,  which  loop 
is  called  a  siphon. 

Safety-valve.  —  All  boilers  are  de- 
signed of  such  strength  that  they  will 
confine  the  steam  at  a  given  pressure,  and 
if  this  pressure  is  exceeded  the  boiler  is  liable  to  burst.  Some 
method  must  be  used  for  keeping  the  steam-pressure  from  rising 
above  this  given  pressure.  The  safety-valve  is  used  for  the 
purpose.  It  consists  of  a  valve  so  arranged  that  it  will  open 
and  let  the  steam  escape  when  the  pressure  for  which  it  was 
set  is  reached.  There  are  two  kinds:  the  weight-and-lever 
safety-valve  and  the  pop  safety-valve.  In  the  former  a  lever 
of  the  third  class  is  used  in  connection  with  a  heavy  weight  for 
retaining  the  steam.  The  pressure  at  which  the  steam  blows 
off  will  depend  on  the  distance  of  the  weight  from  the  fulcrum. 
Fig.  131  shows  this  safety-valve  in  elevation.  The  lever  is 
pivoted  at  C .  The  pressure  of  steam  is  exerted  upon  the  lever 

*  A  =  water-column,  b  =  siphon;  c  =  gauge-cocks;  d  —  gauge-glass. 


FlG.  130 — Water- 
column.* 


T44 


STEAM-POWER. 


at  B.     Then  applying  the  law  of  levers  or  moments  we  have, 
taking  moments  about  C. 


P       s  = 


or 


Wm       wn 

P  = -I -4-  w, , 

s  s  l' 

in   which   P  =  total   upward   pressure    on   the   valve,     W  the 
weight  of  the  ball,  w  the  weight  of  the  lever,  wl  the  weight 


FIG.  131. — Safety-valve. 

of  the  valve  and  spindle,  s  the  distance  from  the  centre  of  the 
fulcrum  to  the  centre  of  the  valve-spindle,  m  the  distance  from 
the  fulcrum  to  the  centre  of  the  ball,  and  n  the  average  lever- 
arm  of  the  weight  of  the  lever  =  the  total  length  divided 
by  2. 

The  pop  safety-valve  gets  its  power  to  hold  steam-pressure 
by  means  of  a  strong  spring  above  the  valve,  which  takes  the 
place  of  the  lever  and  weight  of  the  other  type.  Different 
pressures  are  held  by  increasing  or  decreasing  the  tension  in 
the  spring  by  means  of  a  nut.  Fig.  132  is  an  example  of  this 
type. 

Feed- water. —The  water  out  of  which  steam  is  made  is 
forced  into  the  boiler  against  the  steam-pressure  therein  by  two 
distinct  means;  viz.,  the  feed-pump  and  the  injector.  The 


HEAT  AND  STEAM. 


145 


FIG.  132. — Pop  Safety-valve. 


FIG.  133. — Feed-pump. 


146 


STEAM-POWER. 


STEAM 


feed-pump  puts  water  into  the  boiler  cold  or  at  the  temperature 
at  which  it  receives  it,  while  the  injector  warms  it  in  putting 
it  in.  The  feed-pump  is  used  principally  in  stationary  practice. 
The  injector  may  be  used  on  any  boiler;  but  is  always  found 
on  the  locomotive.  The  feed-pump  is  generally  considered 
more  reliable  than  the  injector,  but  it  takes  up  more  room  and 
is  of  greater  first  cost,  besides  a  greater  cost  for  repairs.  Fig. 
133  shows  a  sectional  cut  of  the  Deane  boiler  feed-pump. 
The  water-piston  is  actuated  by  a  steam-piston.  The  steam 
is  controlled  by  a  common  D-valve.  The  valve-motion  is 
produced  by  a  vibrating  arm. 

The  Injector. — The  water  is  drawn  through  the  injector 
and  fed  into  the  boiler  by  means  of  an  induced  current  pro- 
duced by  the  flow  of  steam  from 
the  boiler  through  the  injector. 
Fig.  134  is  a  very  simple  example 
of  the  injector.  Steam  from  the 
boiler  enters  at  V  and  passes 
through  R  into  the  space  surround- 
ing R  and  S,  where  it  is  partially 
condensed.  The  condensation 
makes  a  vacuum,  and  besides  this 
the  velocity  of  the  steam  and  water 
passing  through  R  and  5  causes 
the  water  to  be  drawn  toward  it 
and  through  S,  F,  and  O  to  the 
boiler.  The  opening  marked 
FIG.  i34.-Penberthy  Injector,  "overflow"  is  brought  into  use 
only  while  starting  the  injector,  that  is,  when  the  water  is  to 
be  lifted  and  put  into  the  boiler,  the  entering  stream  will  be 
blown  to  waste  through  the  overflow  during  a  few  seconds 
necessary  to  exhaust  the  air  in  the  water-supply  pipe.  As 
soon  as  the  steam  which  is  passing  out  of  the  overflow  turns  to 
water  it  shows  that  the  lifting"  of  the  water  has  begun.  The 
above  makes  plain  the  fact  that  for  pumping  water  by  this 
process  there  must  be  a  condensation  as  well  as  a  very  high 


HEAT  AND  STEAM. 


147 


velocity  of  steam.  The  first  requires  that  to  be  injected  the 
water  must  be  cold,  otherwise  the  injector  will  not  work.  The 
high  velocity  of  steam  is  produced  by  the  rapidity  with  which 
it  is  condensed  by  the  cold  water.  The  injector  cannot  be 
used  between  the  feed-water  heater  and  the  boiler  because  of 
the  high  temperature  of  the  feed- water  taken  from  the  former. 
J35  shows  another  injector  of  more  complicated  design, 


FIG.  135- — Monitor  Injector. 

the  Monitor  Injector.  5  is  the  steam- valve,  W  the  water- 
valve,  and  O  the  overflow.  To  start,  first  open  the  steam- 
valve  5  a  little  to  let  the  condensed  water  in  the  steam-pipe 
out  through  the  overflow,  and  shut  again  as  soon  as  clear 
steam  appears.  Next  open  the  water-valve  W,  after  which 
open  the  steam-valve  slowly  and  the  injector  is  at  work.  The 
maximum  temperature  of  water  at  which  this  injector  will  cease 
to  feed  is  about  130°  F.  The  economy  of  the  injector  is  due 
to  the  fact  that  it  returns  to  the  boiler  all  the  heat  of  the  steam 
required  to  operate  it;  nevertheless  it  is  not  as  economical  as 
a  feed-pump  used  in  connection  with  an  exhaust-steam  heater, 
for  the  latter  utilizes  heat  which  would  otherwise  be  wasted. 
Feed-water  Heater. — The  number  of  heat-units  required 


148  STEAM-POWER. 

to  evaporate  a  pound  of  water  is  H  —  I,  in  which  Jf?  =  the 
total  heat  of  evaporation,  and  /  the  heat  of  the  feed-water. 
By  increasing  h  the  heat  required  per  pound  of  steam  is 
reduced.  As  has  just  been  shown,  the  injector  does  this, 
but  at  the  expense  of  steam  taken  from  the  boiler.  The 
exhaust  steam  from  non-condensing  engines,  which  would 
otherwise  exhaust  into  the  atmosphere,  is  generally  used  for 
heating  the  feed-water.  The  exhaust  steam  usually  surrounds 
a  number  of  pipes  through  which  the  feed-water  circulates. 
Fig.  1 36  shows  a  sectional  view  of  a  heater  of  this  type.  The 
feed-water  enters  at  the  bottom  at  the  right  hand  and  passes 
through  the  tubes  to  the  top  and  down  the  left-hand  tubes  and 
out  to  the  boiler.  The  heat  of  the  exhaust  steam  surrounding 
the  tubes  heats  the  water. 

The  Feed-pipe. — The  pipe  which  takes  the  water  from  the 
injector  or  the  feed-pump  to  the  boiler  is  called  the  feed-pipe. 
It  may  enter  the  boiler  at  the  bottom  near  the  back  end,  in 
which  case  the  boiler  is  lower  at  the  back  end,  so  fhat  the  feed- 
pipe may  also  serve  as  a  blow-off  pipe  and  to  drain  the  boiler. 
A  better  method  is  to  introduce  the  feed-pipe  into  the  front  of 
the  boiler  just  above  the  top  row  of  tubes  and  extend  it  a  few 
feet  within  the  boiler.  By  this  means  the  contact  of  the  cold 
water  with  the  hot  plate  of  the  boiler  is  avoided,  thus  avoiding 
damage  to  the  shell  of  the  boiler.  Another  method  is  to  utilize 
the  heat  from  the  chimney-gases  for  heating  the  feed-water. 
Coils  of  pipe  through  which  the  feed-water  passes  on  the  way 
from  the  feed-pump  to  the  boiler  are  placed  so  that  the  flue- 
gases  pass  in  contact  with  them,  thus  heating  the  feed-water. 
This  apparatus  is  called  an  economizer,  of  which  Fig.  137  is  an 
illustration.  Here  the  economizer  is  placed  by  the  side  of  the 
furnace  and  in  the  flue  from  the  back  end  of  the  setting  around 
to  the  stack.  The  feed-pipe  usually  has  two  check-valves  with 
a  gate-valve  between  the  boiler  and  feed-pump. 

Blow-off  Pipe. — When  the  boiler  contains  sediment  due  to 
the  precipitation  from  impure  water  and  the  high  temperatures, 
an  opening  is  made  somewhere  in  the  lowest  part  of  the  boiler. 


HEAT  AND  SJEAM 


149 


A  SURFACE  BLOW 


FIG    136. — Feed-water  Heater. 


STEAM-POWER. 


HEAT  AND  STEAM.  151 

and  the  rush  of  the  steam  towards  this  point  carries  the 
impurities  with  it.  For  this  purpose  the  blow-off  pipe  is  placed 
at  the  lowest  point  of  the  boiler.  By  it  the  boiler  may  also 
be  drained  of  water.  The  blow-off  valve  consists  usually 
of  a  plug-cock.  The  blow-off  pipe  should  be  of  large  diam- 
eter in  order  to  prevent  clogging  up  by  the  acccumulation 
of  solid  matter  in  the  bottom  of  the  boiler*  The  blow-off 
pipe  in  water-tube  boilers  generally  leads  off  from  the  mud- 
drum. 

Dampers. — The  draft  in  a  boiler-furnace  is  regulated  by 
means  of  the  damper,  or  draft-doors.  That  is,  by  closing  the 
draft-doors  the  draft  stops  and  vice  versa.  This  is  frequently 
done  automatically,  by  a  mechanical  device  which  causes  the 
doors  to  close  or  open  according  to  the  variations  of  pressure 
of  the  steam  in  the  boiler. 


PROBLEMS. 

1.  A  Fahrenheit  thermometer  reads   120.      What  h  the  absolute 
temperature? 

2.  A  steam   gauge  read    106.3    pounds  per    square    inch.      The 
barometer  reads  29.84.     Find  the   absolute  pressure  in  pounds  per 
square  inch. 

3.  A  vacuum-gauge  on  a  condenser  reads  26  inches  of  mercury.  Find 
the  absolute  pressure  in  the  condenser,  if  the  barometer  is  29.92  inches. 

4.  Find  the  heat-units  in  a  pound  of  water  at  60°  F. 

5.  Find  the  heat-units  required  to  change  8  pounds  of  water  from 
a  temperature  of  60°  F.  to  a  temperature  202°  F. 

6.  Find   the  heat-units  required  to  convert  60  pounds  of  water  at 
a  temperature  of  100°  F.  into  dry  saturated  steam,  at  a  pressure  of 
85-3  gauge. 

7.  Find   the  heat-units  required  to   convert  20  pounds  of  water 
at  a  temperature  of  70°  F.  into  steam  at  120  pounds  absolute,   con- 
taining 3%  moisture. 

C.  Find  the  heat-units  required  to  convert  i  pound  of  water  at  a 
temperature  of  50°  F.  into  steam  with  a  pressure  of  100  pounds 
absolute  and  a  temperature  of  360°  F. 


152  STEAM-POWER. 

9.  Find  the  volume  of  2  pounds  of  steam  which  has  a  pressure  of 
70.3  pounds  gauge. 

10.  Find  the  weight  of  10  cubic  feet  of  steam  which  has  a  pressure 
of  74.3  pounds  gauge. 

11.  A  boiler  horse-power,  according  to  the  A.S.M.E.  standard,  is 
"  the  evaporation  of  30  pounds  of  water  at  100°  F.  into  steam  at  70 
pounds  gauge  in  one  hour,  or  34 J  pounds  from  water  at   212°  F.  into 
steam  at  212°  F."  in  one  hour.     How  many  B.T.U.s  are  equivalent  to 
one  horse-power  ? 

12.  A  boiler  evaporates  3000  pounds  of  water  per  hour.     The  feed- 
water  has  a  temperature  of  202°   F.  and  the  steam-pressure  is  100 
pounds  absolute.     Find  (a)  the  equivalent  number  of  pounds  (equiva- 
lent evaporation)  that  would  be  evaporated  "from  and  at  212°."     (b) 
the  horse-power  developed. 

13.  A  return  tubular  boiler  has  82  tubes.     The  diameter  of  the 
boiler  is  5  feet,  the  length  is  18  feet.       The  length  of  the  tubes  is  16 
feet  and  their  inside  diameter  is  2^-  inches.     Find  the  heating  surface 
in  square  feet  if  the  setting  allows  f  of  the  shell  in  contact  with  the 
fire. 

14.  What  is  the  rated  horse-power  of  the  above  boiler,  allowing  15 
square  feet  of  heating  surface  per  H.P.  ? 

15.  The  grate  for  the  above  boiler  is  4  feet  6  inches  by  4  feet  6 
inches.     What  is  the  grate  surface  in  square  feet  ? 

1 6.  What  is  the  ratio  of  the  heating  surface  to  the  grate  surface  ? 

17.  On  the  grate  given  above  a  ton  of  coal  is  burned  every  24 
hours.     Find  the  rate  of  combustion. 

1 8.  Find  the  number  of  Ibs.  of  coal  burned  per  hour  per  H.P.  from 
the  above. 

19.  A  furnace  burns  50  Ibs.  of  coal  per  hour.     A  chemical  analysis 
shows  60    per  cent  carbon,  5   per  cent  hydrogen,   and   10  per  cent 
oxygen.     Find  the  number  of  heat-units  generated  per  hour. 

20.  If  3000  Ibs.  of  steam  per  hour  is  required  from  a  boiler,  the 
steam-pressure  being  100  Ibs.  gauge,  and  the  feed-water  temperature 
200°  F.,  how  many  Ibs.  of  coal  per  hour  will  be  burned,  the  heating 
value  of  the  coal  being  13,000  heat-units  per  lb.,  and  the  efficiency  of 
the  boiler  being  60  per  cent  ? 

21.  A  round   chimney  is   to    be   100  feet  high  for   a    200    H.P. 
boiler.     Find  the  necessary  diameter. 


HEAT  AND  STEAM.  1 53 

22.  In  Fig.  131  let  m  be  18  inches,  n  12  inches,  and  s  2$  inches. 
The  valve  weighs  3$  pounds,  the  ball  85  pounds,  and  the  lever  7 
pounds.  The  valve  is  3  inches  in  diameter.  Find  the  pressure,  in 
pounds  per  square  inch,  at  which  the  valve  will  blow  off. 


CHAPTER    XV. 
SIMPLE   STEAM-ENGINE. 

A  STEAM-ENGINE  is  either  reciprocating  or  rotary.  All 
engines,  whether  reciprocating  or  rotary,  are  either  simple-  or 
multiple -expansion  engines,  and  are  also  either  condensing  or 
non-condensing.  Reciprocating  engines  also  are  either  single- 
or  double-acting. 

In  a  reciprocating  engine,  the  steam  gives  to  a  piston, 
operating  in  a  closed  cylinder,  a  back-and-forth  motion.  This 
back-and -forth  or  reciprocating  motion  is  usually,  converted 
into  rotary  motion  by  means  of  a  crank,  but  sometimes,  as  in 
the  case  of  pumps,  steam-hammers,  etc.,  it  is  not  so  converted. 

A  rotary  engine  uses  the  expansive  force  of  steam  to  pro- 
duce rotation  directly,  without  the  interposition  of  cranks, 
pistons,  etc.  This  style  of  engine  is  usually  very  uneconomi- 
cal and  but  little  used.  Recently,  however,  the  steam-turbine 
has  been  developed.  It  runs  at  a  high  rate  of  speed  and  is 
fairly  economical  in  its  use  of  steam.  It  will  be  discussed  in 
the  section  on  steam-turbines,  Chapter  XXII. 

In  a  simple  engine  the  steam  does  its  work  in  one  cylinder, 
and  is  then  exhausted  into  the  atmosphere  or  a  condenser. 

In  a  multiple-expansion  engine  the  steam  is  exhausted  from 
the  first  cylinder  into  a  receiver.  From  the  receiver  it  is  taken 
into  a  second  and  larger  cylinder,  where  it  is  used  a  second 
time.  From  this  second  cylinder  it  may  either  go  to  a  second 
receiver  to  be  used  still  another  time,  or  it  may  go  to  the  con- 
denser, or  exhaust  to  the  atmosphere. 

An  engine  using  the  steam  twice  is  a  compound  engine; 

154 


SIMPLE  STEAM-ENGINE.  155 

one  using  it  three  times  is  a  triple-expansion  engine ;  one  using 
it  four  times  is  a  quadruple-expansion  engine,  etc. 

A  non-condensing  engine  exhausts  directly  into  the  atmos- 
phere. A  condensing  engine  exhausts  into  a  condenser,  where 
the  exhaust  steam  is  condensed  by  means  of  cold  water,  and 
is  then  removed  to  the  atmosphere  by  means  of  a  pump. 

In  a  single-acting  engine  the  steam  acts  only  on  one  side 
of  the  piston.  In  a  double-acting  engine  it  acts  on  both  sides 
of  the  piston  alternately. 

This  chapter  will  treat  only  of  reciprocating  engines. 
Rotary  engines  will  be  discussed  later. 

The  first  engine  to  be  considered  is  the  simple,  double- 
acting,  non-condensing,  D  slide-valve  engine,  shown  in  Figs. 
138  and  i  39.  The  various  parts  are  named  in  the  illustrations. 

The  cylinder  is  a  hollow,  cylindrical  vessel,  closed  at  both 
ends.  The  piston  is  a  disk,  flat  or  otherwise,  which  moves 
inside  the  cylinder  with  a  reciprocating  motion.  The  piston 
is  fitted,  so  that  it  is  steam-tight  within  the  cylinder,  by  means 
of  piston-rings.  These  are  cast-iron  rings,  which  are  split 
diagonally  at  one  point  of  their  circumference,  and  which  are 
sunk  into  grooves  in  the  piston.  When  made,  they  are  turned 
slightly  larger  than  the  diameter  of  the  cylinder,  and  then 
split.  Enough  metal  is  taken  out  at  the  split  so  that  the  rings 
can  be  compressed  to  a  smaller  diameter  than  the  cylinder. 
When  placed  in  the  piston  the  rings  spring  out  against  the 
walls  of  the  cylinder,  making  a  steam-tight  yet  easy  sliding  fit. 
The  cylinder  is  counterbored  at  each  end,  to  facilitate  the 
introduction  of  the  piston. 

Steam  from  the  boiler  enters  the  steam-chest  by  means  of 
the  steam-pipe.  The  D-valve,  so-called  on  account  of  its 
resemblance  to  the  letter  D,  being  in  the  position  shown,  the 
steam  from  the  chest  passes  into  the  steam-port,  and  from 
thence  into  the  cylinder.  The  steam  forces  the  piston  back. 
This  motion  is  transmitted  to  the  fly-wheel  by  means  of  the 
piston-rod,  cross-head  connecting-rod,  and  crank,  and  causes 
the  fly-wheel  to  revolve.  On  the  crank-shaft  of  the  engine 


156 


STEAM-POWER. 


is  placed  the  eccentric.  This  is  a  disk,  eccentrically  placed 
on  the  shaft  and  fastened  to  it.  Around  the  eccentric  is 
placed  the  eccentric- strap.  This  strap  completely  encircles 


the  eccentric,  with  a  sliding  fit,  and  is  attached  to  the  eccen- 
tric-rod. The  D-valve  is  joined  to  the  eccentric-rod  by  means 
of  the  valve-rod  as  shown  in  the  illustration.  The  amount  of 
eccentricity,  or  distance  between  the  centre  of  the  shaft  and 
the  centre  of  the  eccentric,  determines  the  amount  of  move- 


SIMPLE  STEAM-ENGINE. 


157 


ment  of  the  valve ;  the  travel  of  the  valve  is  twice  the  eccen- 
tricity. 

As  the  shaft  rotates,  the  D-valve  is  moved  by  the  eccentric, 


and  at  some  predetermined  point  of  the  stroke  of  the  piston  it 
closes  the  port.  The  steam  is  now  prevented  from  entering 
the  cylinder,  or  is  cut  off.  The  point  in  the  stroke  where  the 
valve  closed  is  the  point  of  cut-off.  The  steam  already 


I58  STEAM-POWER. 

admitted  to  the  cylinder  expands,  nearly  according  to 
Mariotte's  law,  which  is:  The  volume  of  a  gas  varies  inversely 
as  its  pressure,  the  temperature  being  uniform;  or  more  con- 
cisely, p  X  v  =  constant,  and  by  its  expansion,  the  piston  is 
forced  to  the  end  of  the  stroke.  By  the  time  the  stroke  is 
completed,  the  eccentric  has  moved  the  valve  over  so  that 
communication  is  established  between  the  steam -port  and  the 
exhaust-port  by  means  of  the  valve.  By  this  means  the  steam 
is  now  released  from  the  cylinder  and  flows  to  the  atmosphere 
by  way  of  the  steam  port,  valve,  exhaust-port,  and  exhaust- 
pipe.  The  point  in  the  stroke  at  which  the  steam  is  released 
is  called  the  Release  point,  or  simply  the  release. 

At  or  near  the  time  that  the  steam  was  released  from  the 
head  end  of  the  cylinder,*  the  valve  uncovered  the  steam-port 
leading  to  the  crank  end,  thus  admitting  steam  behind  the 
piston.  The  point  of  the  stroke  where  the  valve  uncovers  the 
port,  so  as  to  admit  steam  to  the  cylinder,  is  called  the  point 
of  admission. 

The  piston  is  moved  in  the  opposite  direction  to  that  in 
which  it  started,  by  the  steam  which  is  admitted  behind  it. 
It  drives  the  steam  from  the  head  end  until  the  valve  is  moved 
so  that  the  communication  between  the  exhaust-  and  steam- 
ports  at  the  head  end  is  closed.  Some  steam  remains  in  the 
cylinder,  and  is  compressed  by  the  motion  of  the  piston.  The 
point  of  the  stroke  at  which  the  exhaust-passage  is  closed  is 
called  the  point  of  compression.  When  the  piston  reaches  the 
end  of  the  stroke,  or  usually  just  before,  the  valve  admits  steam 
to  the  head  end  of  the  cylinder  again,  and  the  cycle  of  the 
engine  is  complete. 

The  cylinder  of  the  engine  is  usually  made  of  cast  iron. 
The  walls  are  made  heavy  enough  to  withstand  the  unbalanced 
pressure  of  the  steam  on  the  interior.  The  thickness  of  the 
walls  may  be  determined  by  the  following  formula,  given  by 
Kent: 

/  =  0.0004/2^  -f-  °-3  inch, 

*  The  head  end  of  the  cylinder  is  the  end  away  from  the  crank  of  the 
engine.     The  crank  end  is  the  end  next  to  the  crank. 


SIMPLE  STEAM-ENGINE  159 

where  /  is  the  thickness  of  the  cylinder-wall,  and  D  the 
diameter  of  the  cylinder,  both  in  inches,  and  /  is  the  pressure 
of  steam  in  pounds  per  square  inch. 

The  cylinder-heads,  or  covers,  are  also  of  cast  iron.  They 
are  usually  made  slightly  thicker  than  the  walls  of  the  cylinder. 
Thurston  says  the  excess  over  the  walls  should  not  exceed  25 
per  cent.  Sometimes  the  head  is  stiffened  by  ribs,  radiating 
from  the  centre.  In  this  case  it  is  not  necessary  to  make  the 
cylinder-head  so  heavy.  The  cylinder-heads  are  fastened  to 
the  cylinder  by  means  of  machine-bolts  or  studs.  Studs  are 
preferable  for  a  horizontal  engine.  These  studs  or  bolts  are 
screwed  into  flanges  on  the  cylinder,  which  flanges  are  made 
slightly  heavier  than  the  cylinder-walls.  The  flange  on  the 
head  through  which  they  are  screwed  is  usually  of  the  same 
thickness  as  the  flange  on  the  cylinder. 

The  piston  is  also  usually  built  of  cast  iron.  It  may  be 
cast  in  one  piece  and  the  grooves  for  the  piston -rings  turned 
in  it,  or  it  may  be  built  of  a  number  of  pieces,  fitted  together. 
The  latter  kind,  shown  in  Fig.  140,  is  termed  a  built-up  piston. 
The  piston  should  be  heavy  enough  to  stand  the  difference  of 
pressure  of  the  live  steam  and  that  of  the  steam  which  is  being 
exhausted. 

The  piston-rod  is  made  of  steel  or  wrought  iron.  It  is 
usually  tapered  on  the  piston  end  and  fits  into  a  taper-hole. 
On  the  opposite  side  of  the  piston  it  is  secured  by  a  nut.  It 
passes  through  the  cylinder-head,  through  a  stuffing-box, 
shown  in  Fig.  141,  which  keeps  the  rod  steam-tight.  The 
end  of  the  rod  outside  the  cylinder  is  fastened  to  the  cross- 
head.  The  method  of  fastening  varies  in  different  cases. 
Sometimes  the  rod  is  screwed  into  the  cross-head.  In  locomo- 
tives it  is  tapered  to  fit  a  tapered  hole,  and  a  taper-key  is 
driven  through  it,  from  one  side  of  the  cross-head  to  the  other, 
thus  holding  the  rod  firmly  in  place.  Unwin  gives  the  follow- 
ing formula  for  the  diameter  of  the  piston-rod : 

d  =  bD  Vp, 


i6o 


STEAM-POWER. 


where  d  is  the  diameter  of  the  rod,  and  D  the  diameter  of  the 
cylinder,  both  in  inches;  /  is  the  maximum  unbalanced  pres- 
sure in  the  cylinder  in  pounds  per  square  inch,  and  b  is  a  con- 
stant. For  iron  b  =  .0167;  for  steel  b  =  .0144. 


FIG.  140. — Built-up  Piston.* 

The  cross-head,  shown  in  Fig.  142,  is  often  a  solid  block 
of  wrought  iron  or  steel.  It  serves  to  unite  the  piston-  and 
connecting-rods.  It  is  joined  to  the  connecting-rod  by  means 

*  Bass-Corliss  engine. 


SIMPLE  STEAM-ENGINE. 


161 


of  a  wrist  or  cross-head  pin.  This  is  a  steel  pin  of  generous 
proportions  which  retains  the  connecting-rod  end  in  a  slot  in 
the  back  of  the  cross-head.  The  pin  is  seated  in  the  sides  of 
the  slot,  and  is  usually  stationary,  the  rod  moving  around  it. 


CYLINDER 
HEAD 


FIG.  141.— Stuffing-box. 


FIG.  142. — Cross-head  of  the  Buffalo  Automatic  Cut-off  Engine. 

Sometimes,  however,  it  is  made  a  part  of  the  rod  and  rotates 
in  bearings  in  the  cross-head.  A  rough  rule  for  the  dimensions 
of  cross-head  pins  is  to  make  its  length  from  .25  to  .3  the 
diameter  of  the  piston  and  its  diameter  .18  to  .2  that  of  the 
piston.  The  cross-head  slides  back  and  forth  between  two  bars 


1 62  STEAM-POWER 

termed  guides.  The  wearing  surface  of  the  cross-head  may 
be  lined  with  brass  or  some  anti -friction  metal. 

The  guides  are  two  long,  smooth  surfaces,  placed  parallel 
to  the  axis  of  the  cylinder  at  its  crank  end.  They  guide  the 
cross-head  in  its  proper  path.  The  area  of  the  cross-head  bear- 
ing surface,  according  to  Seaton,  should  be  such  that  the 
bearing  surface  on  which  the  thrust  of  the  connecting-rod  is 
taken  will  admit  of  a  pressure  of  400  Ibs.  to  the  square  inch. 
That  is,  the  area  of  that  portion  of  the  guide  on  which  the 
cross-head  bears  when  the  engine  is  standing  still.  But  for 
good  working  the  surfaces  should  be  made  so  that  this  pressure 
will  not  exceed  100  Ibs.  The  formula  given  for  the  area  of 
the  slides  by  various  authorities  is 

A  =  P  tan  B  +  /0 , 

where  P  is  the  total  unbalanced  pressure,  8  the  angle  whose 
sine  =  £  stroke  of  piston  -r-  length  of  connecting-rod.  If  the 
engine  rotates  in  the  direction  of  the  arrow,  Fig.  139,  the  wear 
will  come  principally  on  the  upper  guide.  If  it  rotates  in  the 
opposite  direction  it  will  come  principally  on  the  lower  one. 
If  the  engine  is  a  reversing  one  the  greatest  wear  will  be  on 
either  guide,  depending  on  the  direction  of  rotation. 

The  connecting-rod  is  a  steel  or  wrought-iron  bar  joining 
the  cross-head  to  the  crank.  In  length  it  is  usually  four  to  five 
times  the  length  of  the  crank.  In  section  it  may  be  either 
circular,  rectangular,  or  of  I  section.  Rods  of  circular  section 
are  sometimes  made  heavier  in  the  middle  than  at  either  end. 
Whitham  gives  for  the  diameter  of  the  connecting-rod  at  the 
middle  the  following  formula: 


where  D  is  the  diameter  of  the  cylinder  in  inches,  /  length  of 
connecting-rod  in  inches,  and  p  is  the  maximum  steam-pres- 
sure in  pounds  per  square  inch.  The  diameter  of  the  rod  at 
its  ends  may  be  seven  eighths  of  the  diameter  at  the  middle. 


SIMPLE  STEAM-ENGINE. 


163 


The  ends  of  the  connecting-rods  are  secured  to  the  crank  and 
cross-head  pins  in  various  ways.  A  brass  bearing  is  placed 
around  the  pins,  and  then  a  strap  passes  over  the  bearing  and 
end  of  the  rod  and  is  secured  in  place  by  a  taper-key,  passing 
through  both  rod  and  strap  as  in  Fig.  143.  In  marine  engines 


FIG.  143. — Connecting-rod  of  the  Porter-Allen  Engine. 


FIG.  144.— Marine  Connecting-rod, 

c'  c" 


FIG.  145. — Solid  Crank  and  Shaft. 

the  brasses  are  generally  secured  to  the  rods  by  bolts  passing 
through  the  brasses,  into  an  end  forged  directly  on  the  rod. 
See  Fig.  144. 

The  crank  may  be  made  in  various  ways.      It  may  be  an 
ordinary  crank,  Fig.  147,  forged  of  wrought  iron  or  steel,  or 


i64 


STEAM-POWER. 


it  may  be  made  in  the  shape  of  a  disk  with  a  crank  pin  set  in 
it  as  in  Figs.  138  and  139.  The  crank  may  be  overhanging 
as  in  Fig.  138,  or  it  may  have  an  outboard  bearing.  In  this 
case  another  disk  or  arm  is  placed  parallel  to  the  first,  as 
shown  in  Figs.  145  and  146,  with  the  crank-pin  set  between 


FIG.  146. — Crank  of  the  Straight-line  Engine. 

them.  This  disk  or  arm  is  forced  on  a  shaft  which  runs  in  a 
bearing  outside  of  the  engine.  The  diameter  of  the  crank-pin 
is  found  by  the  formula  given  by  Unwin: 


where  /  is  the  allowable  stress  on  the  metal,  being  about 
9000  Ibs.  for  iron.  P  is  the  maximum  load  on  the  piston, 
/and  d  are  the  length  and  diameter  of  the  pin  respectively  in 


inches.      The   ratio    -=  is    assumed.      If  either  the   length    or 
diameter  is  given  the  formula  will  read : 

#^V-/2ilV5PZ 


SIMPLE  STEAM-ENGINE.  165 

For  the  length  of  the  crank-pin  Whitham  grves-nh 

I.H.P. 

/=  .9Q75/      L     , 

in  which  /  is  the  coefficient  of  friction  of  the  pin ;  this  coeffi- 


FIG.  147.— Crank. 


cient  may  be  taken  as  .03  to  .05  if  the  pin  is  perfectly  lubri- 
cated; if  not,  take/=  .08  to  .1.      L  is  the  length  of  stroke  of 


1 66  STEAM-POWER. 

the    engine    in    feet,    and    I.H.P.    represents    the    theoretical 
indicated  horse-power  of  the  engine. 

The  crank-shaft  carries  the  fly-wheel,  and  when  turned  by 
the  crank,  it  causes  the  fly-wheel  to  revolve  with  it.  It  should 
be  made  of  wrought  iron  or  steel.  Its  diameter  should  be, 
according  to  Unwin,  , 


H        .,-/   LH-P- 

a  =  a\  I  -n  ^  n»  » 


where  R.P.M.  represents  the  revolutions  per  minute  and  a  is 
constant,  depending  on  the  strength  of  the  material  and  the 
factor  of  safety.  He  gives  a  =  3.294  for  wrought  iron  and 
a  =  2.877  f°r  steel. 

If  the  engine  is  direct-connected  to  an  electric  generator, 
the  armature  of  the  generator  is  carried  by  the  crank-shaft. 
The  shaft  in  this  case  must  be  made  very  much  larger  than 
the  diameter  determined  by  the  formula,  to  decrease  the  deflec- 
tion of  the  shaft  due  to  the  weight  of  the  armature  as  much  as 
possible. 

The  fly-wheel  of  the  engine  serves  to  preserve  a  uniform 
speed  of  rotation  of  the  engine  during  a  revolution.  It  stores 
up  energy,  or  gives  it  off  in  accordance  with  the  fluctuations  of 
the  load.  The  fly-wheel  is  sometimes  used  as  a  band-wheel, 
by  means  of  which  the  engine  transmits  power.  If  the  engine 
runs  faster  than  its  usual  rate,  as  may  be  caused  by  the 
governor-belt  breaking,  the  fly-wheel,  if  not  strong  enough, 
may  burst  from  centrifugal  force.  Fly-wheels  should  be 
designed  so  as  to  withstand  a  moderate  increase  in  speed. 
The  maximum  velocity  at  which  a  cast-iron  fly-wheel  should 
be  run  is  6000  feet  per  minute.  Then  the  diameter,  D,  of  the 
wheel  will  be 

6000       1910 
~^R''     ~R~' 

R  being  the  number  of  revolutions  per  minute. 


SIMPLE  STEAM-ENGINE. 


167 


The  eccentric  is  a  flat  disk  of  cast  iron,  set  eccentric  with; 
the  shaft.  The  amount  of  eccentricity, 
e,  Fig.  148,  determines  the  travel  of 
the  valve.  It  may  be  either  keyed  to 
the  shaft  or  attached  by  means  of  set- 
screws.  The  eccentric-strap  which 
fits  around  the  eccentric  is  made  in 
two  pieces  usually.  The  two  pieces 
are  joined  with  bolts ;  the  strap  is  fitted 
so  that  the  eccentric  may  rotate  freely 
FIG.  148.— Eccentric.  within  it,  and  yet  have  no  lost  motion. 
The  eccentric-rod  is  fastened  to  the  eccentric-strap  usually  by 
means  of  bolts,  passing  through  the  rod  and  strap.  It  serves 
to  communicate  motion  to  the  slide-valve,  by  means  of  the 
valve-rod. 

The  valve-rod  is  a  steel  or  wrought-iron  rod,  which  moves 
the  slide-valve.  One  end  is  attached  to  the  valve,  the  rod 
usually  passing  through  the  valve,  by  a  nut  on  each  side  of  the 
valve.  The  rod  passes  through  the  steam-chest  through  a 
stuffing-box,  similar  to  that  used  on  the  piston-rod.  The  rod 
usually  joins  the  eccentric-rod  by  means  of  a  rocker.  The 
valve-rod  may  be  made  one  third  the  diameter  of  the  piston- 
rod. 

The  steam-chest  is  a  closed  box,  into  which  the  steam  first 
passes  from  the  boiler.  It  may  be  either  rectangular  or  cir- 
cular. The  chest  may  be  cast  solid  with  the  cylinder  or  bolted 
to  it.  Its  position  with  regard  to  the  cylinder  varies.  It  is 
usually  placed  on  the  side  of  stationary-engine  cylinders  and 
on  top  of  locomotive  cylinders.  Sometimes  it  is  placed  beneath 
the  cylinder.  The  same  formula  applies  to  the  thickness  of 
the  steam-chest  walls  as  to  the  walls  of  the  cylinder,  both 
being  subject  to  the  same  pressure.  The  bottom  of  the  chest  is 
a  wall  of  the  cylinder.  There  are  three  openings  in  the  bottom, 
which  is  made  a  plane  surface.  The  two  smaller  of  these  open- 
ings are  the  steam-ports  which  lead  to  the  cylinder.  The  third 
and  larger  one  is  the  exhaust-port,  which  communicates  with 


1 68  STEAM-POWER. 

the  atmosphere.  The  length  of  the  steam-ports  is  usually 
made  2  inches  less  than  the  diameter  of  the  cylinder.  The 
area  is  found  as  follows :  Let  A  be  the  area  of  the  piston  in 
square  feet,  let  L  be  the  stroke  in  feet.  Let  the  engine  make 
N  revolutions  per  minute.  Then  the  volume  of  steam  in  cubic 
feet  required  to  fill  the  cylinder  in  one  stroke  will  be  V  =  LA  ; 
in  ^revolutions  the  volume  required  will  be  V  =  2LAN.  Live 
steam  is  allowed  a  velocity  of  6000  feet  per  minute  and  exhaust 
'steam  a  velocity  of  4000  feet.  The  steam-port  has  to  convey 
exhaust  as  well  as  live  steam,  hence  calculations  must  be  made 
for  the  exhaust  steam.  Hence  the  area  of  the  port  to  carry 

2LAN 

the  exhaust  steam  away  is  -       — . 

4000 

The  wall  separating  the  ports  is  called  the  bridge.  If  the 
bridge  is  made  too  narrow,  the  valve  will  travel  over  it,  and 
allow  steam  to  pass  into  the  atmosphere  from  the  steam- 
chest.  Hence  the  bridge  must  be  made  so  wide  that  there  is 
no  possibility  of  such  a  waste. 

The  exhaust-port  communicates  with  the  atmosphere  by 
means  of  a  pipe.  This  pipe  is  termed  the  exhaust-pipe,  and 
should  be  laid  with  as  few  bends  as  possible.  The  area  of  the 
exhaust-port  should  be  33  per  cent  greater  than  the  area  of 
the  steam-port  at  the  valve-seat.  It  should  gradually  increase 
in  area  until  it  is  50  per  cent  greater  at  the  entrance  to  the 
exhaust-pipe. 

The  valve  of  the  engine  will  be  discussed  in  a  later  chapter, 
under  the  head  of  "  Valves  and  Valve-gears." 

The  bed  of  the  engine  is  a  heavy  cast-iron  frame,  which  is 
bolted  firmly  to  foundations  of  masonry  or  concrete.  It  has 
various  forms  with  different  makers.  The  cylinder  of  the 
engine  is  sometimes  cast  solid  with  the  bed  and  sometimes  is 
bolted  on.  The  guides  are  also  sometimes  cast  on  the  bed, 
and  sometimes  not.  The  frame  usually  carries  the  crank-shaft 
bearings,  Fig.  149. 

The  governing,  or  regulation  of  the  speed  of  the  engine,  is 
accomplished  by  means  of  the  governor,  shown  in  Fig.  150. 


SIMPLE  STEAM-ENGINE. 


169 


FIG.  149. — Crank-shaft  Bearing  of  the  Houston,  Stanwood  Sf  Gamble 

Engine. 


FIG.  150.— Governor. 


T  7  o  S  TEAM-POWER. 

If  the  load  on  the  engine  was  suddenly  lightened,  and  the 
steam-supply  remained  the  same,  the  engine  would  commence 
to  run  faster  and  if  not  checked  might  cause  its  fly-wheel  to 
burst.  Its  speed  is  checked  by  the  governor.  When  the  engine 
speeds  up,  the  balls  GG,  driven  through  the  pulley  E,  and 
bevel-gears  F  and  Z),  by  a  belt  to  the  crank-shaft,  fly  out  from 
centrifugal  force.  As  they  fly  out  they  rotate  about  the  pivots 
KK.  The  rod  H  is  depressed,  partly  closing  the  valve  C  in 
the  steam-pipe  AB  and  shutting  off  the  steam-supply.  The 
decrease  in  the  steam-supply  causes  the  engine  to  run  slower. 
If  it  runs  too  slowly  the  balls  drop  and  open  the  valve  C,  thus 
admitting  more  steam  to  the  engine.  The  hand-wheel  and 
spring  at  T  serve  to  regulate  the  speed  at  which  the  governor 
will  act.  A  governor  such  as  has  been  described  is  known  as 
a  throttling  governor. 

Clearance  is  the  volume  contained  between  the  piston  and 
the  end  of  the  cylinder  when  the  piston  is  at  the  end  of  the 
stroke  plus  the  volume  of  the  steam-passage  or  port.  The 
clearance  is  prejudicial  to  the  heat  efficiency  of  an  engine 
because  it  preserves  a  volume  of  steam  which  is  not  active  and 
which  is  subject  to  condensation.  By  so  doing  it  increases 
the  amount  of  steam  required  to  do  a  given  amount  of  work. 
It  varies  according  to  the  make  of  the  engine  from  2  per 
cent  to  12  per  cent.  Back-pressure  is  the  resistance  on  the 
side  of  the  piston  opposite  the  live  steam  and  is  due  to  the 
pressure  of  the  atmosphere  plus  the  resistance  of  the  exhaust 
steam  on  passing  out  through  the  exhaust-pipe  which  offers 
friction.  An  engine  should  have  as  little  back-pressure  as 
possible. 

The  stroke  of  an  engine  is  the  distance  passed  through  by 
the  piston  in  one  movement  in  one  direction  and  is  approxi- 
mately equal  to  the  length  of  the  cylinder  minus  the  thickness 
of  the  piston.*  There  are  two  strokes  to  each  revolution  of  the 

*  "  Piston  displacement "  is  an  expression  for  the  volume  swept  over  by  the 
piston.     For  one  stroke,  on  head  end,  it  is  — •= in  which  D  is  the  diam- 

eter of  the  piston  in  inches  and  L  the  length  of  stroke  in  inches.  Clearance  is 
e:  p  essc  1  in  per  cent  of  this  volume. 


SIMPLE  STEAM-ENGINE.  171 

crank-shaft.  For  a  given  velocity  of  piston  a  higher  speed  of 
rotation  may  be  had  by  making  the  stroke  short  ar.d  a  slow 
speed  ty  makirg  the  stroke  long.  The  velocity  of  the  piston 
is  equal  to  the  length  of  the  stroke  multiplied  by  the  number 
of  strokes  per  minute. 

The  foregoing  is  a  discussion  of  a  simple  non-condensing 
engine.  All  that  would  be  necessary  to  convert  the  engine 
into  a  condensing  engine  would  be  to  connect  the  exhaust- 
pipe  to  a  condenser  having  an  adequate  supply  of  cold  water. 

To  convert  the  engine  to  a  multiple-expansion  engine,  it 
would  be  necessary  to  provide  the  requisite  number  of  cylinders 
with  volumes  of  the  proper  ratio,  and  the  receivers.  Com- 
pound and  multiple-expansion  engines  will  be  treated  sep- 
arately. 

The  formulae  given  in  this  chapter  apply  in  the  main  to  the 
essential  parts  of  all  reciprocating  engines.  The  only  difference 
between  the  engine  just  described  and  a  Corliss  or  automatic 
cut-off  engine  is  in  the  valve-gear  and  governing.  Otherwise 
both  in  construction  and  operation  they  are  identical.  Such 
changes  in  the  given  formulae  as  are  necessary  to  suit  these 
special  cases  will  be  made  at  the  proper  time. 

PROBLEMS. 

1.  An   engine    i8"X24"    makes    250    R.P.M.      Find    the   piston 
speed  in  F.P.M. 

2.  Draw  a  sketch  of  a  steam-engine  and  name  all  the  parts. 

3.  Draw  a  sketch  showing  the  position  of  the  valve,  piston,  and 
port  for  each  of  the  four  events  of  the  piston  stroke.    Indicate  the 
direction  of  motion  of  the  piston  and  valve. 

4.  An  engine  makes  300  R.P.M.     Determine  the  maximum  diam- 
eter of  cast-iron  fly-wheel  that  will  be  safe. 

5.  Determine  the  dimensions  cf  he  steam  and  exhaust  ports  an  1 
pipes  for  a  io"Xi27/    engine   running   at  150  R.P.M.     Assume  the 
length  of  the  ports  as  8  inches. 

6.  Find  the  diameter  of  a  steam-pipe  that  will  pass  5000  pounds 
of  steam,  at  a  pressure  of  100  pounds  absolute,  per  hour.     Velocity  of 
flow,  6000  F.P.M. 

NOTE. — Find  volume  per  hour  by  using  column  8  of  the  steam  table. 


172  5  TEAM-POWER. 

7.  Examine  the  different   connecting-rod  ends  shown  on  page  163 
and   note  the  effect  upon  the  length  of  the  rod  when  adjustment  is 
made  for  wear. 

8.  An    engine    is    io"xi2".      Piston-rod    ij    inches.      Find    the 
piston  displacement,  in  cubic  feet,  for  head  end  (H.E.)  and  crank  end 
(C.E.). 

9.  If  in  the  engine  of  problem  8,  6  pounds  of  water  were  required 
to  fill  the  crank-end   clearance  space  and  7  pounds  for  the  head-end 
clearance  space,  find  the  clearance  in  per  cent  for  each  end. 

10.  Same  engine  as  in  problems  8  and  9.     Find  the  volume  back 
of  the  piston  in  cubic  feet. 

(a)  When  it  is  at  40%  of  H.E.  stroke. 

(b)  When  it  is  at  40%  of  C.E.  stroke. 


CHAPTER    XVI. 
AUTOMATIC   CUT-OFF   ENGINES. 

HIGH-SPEED    ENGINES. 

AUTOMATIC  cut-off  engines  are  of  two  kinds :  I .  Long-stroke 
engines,  having  a  moderate  rotative  speed,  say  about  60  to 
1 20  revolutions  per  minute.  The  Corliss,  Brown,  and  Greene 
engines  are  in  this  class.  2.  Short-stroke  engines  having  a 
high  rotative  speed,  200  revolutions  per  minute  and  upwards. 
The  Buckeye,  Porter- Allen,  and  Ball  &  Wood  engines  are  in 
this  class. 

The  high-speed  automatic  cut-off  engine  is  that  type  in 
which  the  regulation  of  the  speed  of  the  engine  is  effected  by 
changing  the  travel  of  the  valves  in  such  a  manner  as  to  con- 
trol the  time  of  admission  and  cut-off  of  steam  from  the  steam- 
chest  into  the  cylinder.  This  is  a  modern  type  of  engine 
which  is  run  at  a  high  speed.  The  high  speed  does  not  mean 
necessarily  high  piston-speed  but  high  rotative-speed  by  means 
of  a  very  short  stroke ;  the  diameter  being  in  many  cases  equal 
to  or  greater  than  the  stroke.  This  means  a  short  engine,  if 
we  assume  that  the  length  of  an  engine  is  always  equal  to  four 
times  the  stroke,  which  is  an  average  value  if  the  length  of  the 
connecting-rod  is  taken  as  two  and  one  half  times  the  stroke. 

The  Buckeye  engine  shown  in  Fig.  151  is  an  example  of 
this  type.  The  increasing  or  decreasing  of  the  number  of 
revolutions  for  a  sudden  change  of  load  amounts  to  about  I  per 
cent  and  the  change  is  for  a  few  revolutions  only. 

The  greatest  source  of  trouble  with  high-speed  automatic 
engines  is  the  heating  of  the  main  bearings,  caused  by  the  high 

'73 


STEAM-POWER. 


FIG.  151.  — Buckeye  Engine.     Section  through  Valve  and  Cylinder. 


FIG.  152. — Watertown  Engine.     Section  through  Valve  and  Cylinder. 


AUTOMATIC  CUT-OFF  ENGINES.  I? 5 

speed  of  rotation.  For  this  reason  large  bearings,  well  oiled, 
must  be  provided. 

On  account  of  the  comparatively  large  diameter  of  these 
engines,  the  clearance  is  large,  about  5  to  10  per  cent.  The 
mean  back-pressure  is  3  to  4  Ibs.  above  atmospheric  pressure. 

This  type  is  fairly  economical  in  its  use  of  steam;  it  occu- 
pies small  space  and  regulates  well  but  requires  careful  atten- 
tion, especially  to  bearings.  The  valve  in  this  engine  is 
generally  balanced  and  multiple-ported  as  shown  in  Fig. 
152,  in  order  to  give  a  large  port-opening  with  a  short  travel 
of  the  valve.  Here  it  should  be  remembered  that  the  steam 
has  two  openings  through  the  valve  into  the  steam-port, 
making  an  ample  area  for  the  steam  to  pass  through  without 
being  retarded.  Also  the  steam  enters  above  and  below  the 
valve,  producing  a  balance  and  preventing  the  friction  of  the 
valve  against  the  seat  caused  by  steam-pressure  upon  one  side 
onlyv 

If  is  seen  that  when  the  left  edge  of  the  valve  moves  to  the 
right:  until  it  passes  the  left-hand  steam-port  there  is  a  double 
port-opening. 

Some  engines  also  use  an  auxiliary  valve,  in  connection 
with  the  main  valve,  to  control  the  cut-off  more  fully  than  is 
possible  with  a  single  valve.  The  Buckeye  engine  uses  such 
a  valve ;  it  is  shown  in  Fig.  151. 

Piston- valve. — Another  form  of  balanced  valve  used  on 
this  type  of  engine  is  the  piston-valve,  of  which  Fig.  153  is  an 
illustration.""  In  this  case  the  steam- enters  in  a  direction  which 
is  the  reverse  of  that  with  the  ordinary  valve ;  that  is,  it  comes 
into  the. cylinder  through  the  middle  and  exhausts  through  the 
hollow  valve  and  out  at  the  ends.  This  is  evidently  a  balanced 
valve,  ifie  pressure  being  equal  on  all  sides. 

The-governor  of  an  automatic  engine  is  placed  in  the  fly- 
wheel as:  shown  in  the  illustration  of  the  Straight-line  Engine, 

*  The  piston-valve  here  spoken  of  controls  the  passage  of  the  steam 
into  and  out  of  the  small  cylinder.  The  valve  of  the  large  cylinder  is  of 
the  ordinary  balanced  type. 


i76 


STEAM-POWER. 


Fig.  1 54.      Its  construction  will  be  discussed  more  fully  in  the 
chapter  on  "Valve  Motions." 

However,  it  may  be  proper  to  say  here  that  the  mechanism 


of  the  governor  and  eccentric  is  such  that,  for  an  increase  in 
the  speed  of  the  engine,  the  travel  of  the  valve  is  made  less 
and  the  cut-off  occurs  earlier,  causing  a  diminution  of  speed; 


AUTOMATIC  CUT-OFF  ENGINES.  177 

for  a  diminution  of  the  speed  the  cut-off  occurs  later.  This 
arrangement  causes  each  stroke  to  use  just  what  steam  is 
necessary  for  that  stroke  and  no  more,  the  quantity  depending 
upon  the  load. 

CORLISS    ENGINES. 

By  the  pure  Corliss  type  is  meant  an  engine  having  four 
rotary  valves  for  the  control  of  the  steam,  two  for  admission 
and  two  for  exJiaust  (see  Fig.  156).  Under  the  Corliss  type  are 
generally  included  all  those  engines  whose  valves  are  rotary 


FIG.  154. — Governor  of  the  Straight  line  Engine. 

in  their  motion  or  which  have  more  of  the  pure  Corliss  charac- 
teristics than  of  the  other  types.  These  engines  have  a  high 
piston-speed  but  a  slow  rotary  speed.  This  is  effected  by  a 
comparatively  long  stroke.  The  average  ratio  of  the  diameter 
to  the  stoke  is  one  half.  A  small  diameter  with  short  ports 


STEAM-POWER. 


bfi 

w 


AUTOMATIC  CUT-OFF  ENGINES. 


179 


means  a  small  clearance,  which  is  from  I  to  5  per  cent.  Cor- 
liss engines  usually  make  about  100  revolutions  per  minute  or 
less.  The  system  of  valves  for  each  end  of  the  cylinder  makes 


it  possible  to  cut  off  the  steam  to  suit  the  requirements  of  the 
load  without  changing  the  amount  of  compression,  as  is  neces- 
sary with  the  single  slide-valve. 


l8o  STEAM  POWER. 

Under  varying  loads,  the  Corliss  engine  acts  precisely  the 
same  as  the  high-speed  automatic  engine.  The  governor 
alters  the  valves,  so  that  the  time  of  cut-off  occurs  earlier  or 
later  in  the  stroke,  according  to  whether  the  load  is  decreased 
or  increased,  thus  admitting  to  the  cylinder  the  amount  of 
steam  necessary  to  do  the  work. 

The  mean  back-pressure  for  this  type,  on  account  of  the 
slow  speed,  is  small,  being  from  I  to  3  Ibs.  per  square  inch 
above  atmospheric  pressure. 

This  type  is  the  most  economical  of  the  three  types  dis- 
cussed in  the  use  of  steam,  but  it  takes  more  skill  to  keep  it  in 
order  than  do  the  others,  for  the  reason  that  it  has  more  parts, 
some  of  them  being  very  delicate. 

The  long  stroke  gives  the  engine  great  length  and  it  is  of 
high  first  cost. 

The  arrangement  of  the  four  valves  is  shown  in  elevation 
in  Fig.  155,  and  in  section  in  Fig.  156.  The  valves  are  of 
the  form  shown  in  Fig.  156  and  are  rotated  by  the  valve-rods. 
These  valve-rods  acquire  their  motion  from  the  wrist-plate 
which  is  partially  rotated  about  its  centre.  This  rotation  is 
accomplished  by  means  of  the  ordinary  eccentric.  The  eccen- 
tric is  assisted  in  the  movement  of  the  valves  by  the  dash-pots, 
shown  in  Fig.  155.  These  are  used  in  order  to  give  a  quick 
shutting  of  the  admission-valves,  whereby  the  port  is  given  a 
wide  opening  up  to  the  time  of  cut-off,  and  this  prevents  wire- 
drawing. The  governor  is  usually  of  the  weighted-ball  type 
and  controls  the  time  of  cut-off,  according  to  the  speed  of  the 
engine.  It  is  connected  to  the  valves  by  means  of  the  rods  as 
shown  in  the  diagram.  The  action  of  the  valves  and  governor 
will  be  more  fully  discussed  in  the  chapter  on  "Valves  and 
Valve-gearing." 


CHAPTER    XVII. 
INDICATORS. 

THE  indicator  is  an  instrument  used  for  determining  the 
actual  amount  of  work  that  an  engine  is  performing,  besides 
giving  other  information  as  to  the  conditions  of  working,  such 
as  the  operation  of  the  valves,  etc. 

The  diagram  obtained  by  the  use  of  the  indicator  is  called 
the  indicator-card. 

Fig.  157  shows  in  section  the  Tabor  indicator,  with  a 
reducing  attachment.  It  comprises  a  paper-drum  B  on  which 
blank  paper  is  held  by  means  of  two  clips;  a  cylinder  M  in 
which  works  a  steam-tight  piston  connected  to  a  piston-rod ; 
this  piston-rod  connects  at  the  top  with  a  lever  which  carries  a 
pencil.  The  paper-drum  is  connected  by  a  suitable  reducing 
motion  to  the  cross-head  of  the  engine.  As  the  piston  makes 
a  stroke  the  paper-drum  is  turned  on  its  axis  by  the  pull  of  the 
cord.  A  strong  spring  on  the  inside  of  the  drum  causes  it  to 
make  its  backward  movement.  The  cylinder  M  is  connected 
by  steam-piping  £  inch  in  diameter  to  the  end  of  the  engine- 
cylinder.  Between  the  piston  of  the  indicator  and  the  upper 
end  of  the  cylinder  in  the  space  marked  M  is  placed  a  spring 
of  known  strength,  which  offers  a  measured  resistance  to  the 
upward  movement  of  the  pencil.  The  steam  from  the  engine- 
cylinder  enters  the  indicator  at  Z,  pushes  the  piston  up,  and 
this  in  turn  causes  the  pencil  to  rise.  At  the  same  time  the 
cord  causes  the  paper-drum  to  revolve.  By  means  of  the 
system  of  levers  attached  to  the  pencil-lever,  the  pencil  is 
made  to  move  in  a  straight  line  parallel  to  the  axis  of  the 

181 


182 


STEAM-POWER. 


drum.  When  the  pencil  is  at  rest,  the  line  made  by  pressing 
the  pencil  to  the  paper  and  revolving  the  drum  should  be 
parallel  to  the  base  of  the  drum.  When  the  pencil  is  pressed 


FIG.  157. — Tabor  Indicator. 

against  the  paper,  it  makes  a  line  every  point  of  which  repre- 
sents at  once  the  pressure  in  the  engine-cylinder  and  the  posi- 
tion of  the  engine-piston  within  the  cylinder.  By  shutting  off 
the  indicator  from  the  steam  of  the  engine,  opening  connec- 
tion from  the  indicator  to  the  atmosphere  and  pressing  the 
pencil  to  the  paper,  a  line  parallel  to  the  base  of  the  drum  is 


INDICATORS.  183 

made,  called  the  atmospheric  line.  The  pressure  of  the  steam 
as  shown  on  the  indicator-card  may  be  referred  to  this  line. 
The  springs  used  in  the  cylinder  of  the  indicator  are  num- 
bered according  to  their  strength;  that  is,  a  No.  40  or  40- 
scale  spring  is  one  which  allows  a  movement  of  the  pencil  of 
I  inch  for  a  pressure  of  40  Ibs.  per  square  inch. 

The  following  are  the  prinicipal  conditions  required  in  a 
good  indicator: 

The  line  made  by  pressing  the  pencil  to  the  paper  and 
keeping  the  pencil  at  rest  while  the  paper-drum  revolves  should 
be  perpendicular  to  the  line  made  by  keeping  the  drum  at  rest 
and  moving  the  pencil. 

For  equal  amounts  of  increase  in  t.ie  pressure  the  pencil 
should  rise  equal  distances. 

The  spring  should  be  tested  while  hot.  The  tension  of  the 
spring  to  be  used  in  the  indicator  will  depend  upon  the  speed 
of  the  engine  and  the  pressure  of  steam  used.  Strong  springs 
should  be  used  for  high  speeds  and  high  pressures  and  weaker 
ones  for  low  speeds  and  low  pressures.  This  difference  in 
strength  is  made  partly  on  account  of  the  effects  of  inertia. 

The  indicator  should  be  as  light  as  is  consistent  with  the 
proper  strength,  and  no  joints  should  be  tight  enough  to  cause 
the  least  binding. 

The  cord  should  be  small  and  yet  not  small  enough  to 
allow  it  to  stretch 

In  taking  the  cards  from  an  engine  it  is  necessary  to  take 
the  cards  from  the  two  ends  at  precisely  the  same  time  or  as 
nearly  so  as  possible  in  order  that  the  relations  of  the  condi- 
tions in  the  two  ends  may  be  shown  correctly.  This  can  be 
done  by  the  use  of  two  indicators,  one  on  each  end,  but  one 
indicator  may  be  used  for  one  cylinder  with  the  arrangement 
shown  in  Fig.  158. 

Reducing  Motions. 

The  paper-drums  for  indicators  are  usually  \\  or  2  inches 
in  diameter.  It  is  desirable  that  the  length  of  the  card  be  less 


184 


STEAM-POWER. 


INDICATORS. 


185 


than  the  circumference,  hence  the  lengths  of  the  cards  usually 
taken  with  the  above  two  sizes  are  usually  3  and  4  inches, 
respectively.  As  the  length  of  the  stroke  of  the  engine  is 
many  times  the  length  of  either  one  of  these,  it  is  evident  that 
some  reducing  motion  must  be  used  between  the  cross-head 
and  the  indicator.  Fig.  158  shows  the  pendulum-reducing 
motion  in  which  the  length  of  the  cord  depends  upon  the  dis- 
tance from  the  fixed  pivot  to  the  point  where  the  string  is 
tied.  The  pendulum  is  caused  to  swing  by  being  fastened 
to  the  cross-head  by  a  link.  In  an  indicator  reducing  motion 
the  cord  should  lead  off  from  the  reducing  motion,  for  a  short 
distance  at  least,  parallel  to  the  axis  of  the  engine. 

The  Pantograph,  or  lazy  tongs,  is  shown  in  Fig.  159.  It 
consists  of  a  number  of  wooden  links  pivoted  together  as 
shown.  The  end  A  is  fastened  to  the  cross-head  of  the  engine 


FIG.  159. 

and  the  other  end  B  to  any  stationary  point.  The  cord  leads 
off  from  the  point  E  on  the  link  CD.  The  point  E  must  be 
on  the  centre  line  AB. 

NOTE. — The  most  convenient  and  most  improved  reducing  motion  of 
those  here  given  is  that  shown  in  Fig.  157  which  is  attached  directly  to 
the  indicator.  The  reduction  of  motion  is  produced  through  the  worm  R. 


i86 


STEAM-POWER. 


TAKING    THE    CARD. 

After  the  reducing  motion  and  indicator  have  been  con- 
nected, the  cylinder  of  the  indicator  should  first  be  warmed  by 
turning  on  the  steam,  after  which  the  steam  is  turned  into  the 
indicator-cylinder,  first  from  one  end  of  the  engine-cylinder 
and  then  from  the  other  end,  pressing  the  pencil  to  the  paper 
in  each  case  for  an  instant. 

The  steam  should  then  be  shut  off  from  the  indicator,  and 
an  atmospheric  line  taken.  The  atmospheric  line  should  be 
taken  by  disconnecting  the  string  from  the  reducing  motion, 
and  pulling  it  by  hand,  so  that  the  drum  makes  a  complete 
revolution.  If  this  is  not  done  the  atmospheric  line  will  be  of 
the  same  length  as  the  card,  which  is  not  desirable. 

The  following  data  should  be  placed  on  every  card :   Date, 

time,  revolutions  per  minute,  gauge-pressure,  length  of  stroke, 

diameter  of  piston,  diameter  of  piston-rod ;  and  the  card  should 

1 


FIG.  160. — Indicator-card.  1-2,  steam-line  ;  2,  point  of  cut-off  ;  2-3,  ex- 
pansion-line ;  3,  point  of  release  ;  4-5,  back-pressure  line  ;  5,  point 
of  compression  ;  5-6,  compression-line  ;  6,  point  of  admission  ;  AB, 
atmospheric  line. 

also  be  marked  so  as  to  show  whether  it  is  from  the  head  or 
crank-end  of  the  cylinder. 

Fig.  1 60  shows  a  typical  indicator-card  in  which  the  names 
of  the  points  and  parts  are  given. 

It  should  be  kept  in  mind  that  vertical  distances  represent 


INDICATORS. 


187 


pressures  and  that  horizontal  distances  represent  volumes; 
that  is,  in  Fig.  160  the  point  D  shows  that  the  piston  is  at  the 
middle  of  its  stroke,  passing  from  left  to  right  and  that  the 
pressure  in  the  cylinder  at  that  part  of  the  stroke  is  represented 
by  the  distance  CD.  The  average  height  may  be  found  by 
dividing  the  area  of  the  card  as  determined  by  a  planimeter  by 
the  length,  or  it  may  be  done  by  the  method  shown  in  Fig. 
161,  by  dividing  the  card  into  a  number  of  rectangles,  finding 


FIG.  161. 

the  middle  height  of  each  rectangle  as  shown  by  dotted  lines, 
adding  together  the  heights  thus  found  and  dividing  by  the 
number  of  rectangles.  This  average  height  multiplied  by  the 
scale  of  the  spring  gives  the  average  pressure  per  square  inch 
of  the  steam  in  the  cylinder  during  the  whole  stroke,  and  is 
usually  called  the  Mean  Effective  Pressure^  or  M.E.P. 

Horse-power. — The  work  done  in  a  cylinder  in  foot-pounds 
per  minute  is  equal  to  the  average  pressure  on  the  piston  in 
pounds  multiplied  by  the  distance  moved  through  by  the  piston 
in  one  minute,  that  is,  Work  =  0F,  in  which  0  —  the  total 
pressure  on  the  piston  and  V  =  velocity  of  piston  in  feet  per 
minute. 

Let  P  =  the  M.E.P.,  L  the  length  of  the  stroke  in  feet,  A 
the  area  of  the  piston  in  square  inches,  N  the  number  of  strokes 
per  minute,  and  H.P.  the  horse-power;  then 

V=LN.      < 


i88  STEAM-POWER. 

and 

P  X  A  x  L  X  N      PLAN 


H.P.  = 


33,000  33»°°o' 


The  area  of  the  piston  is  different  in  the  two  ends  of  the 
cylinder,  owing  to  the  presence  of  the  piston-rod  in  the  crank- 
end.  The  area  of  the  rod  should  be  calculated  and  subtracted 
from  the  area  of  the  piston. 

Calculation  .  of  the  Weight  of  Steam  per  hour  per  H.P. 
from  the  Indicator  Card. — Theoretically,  the  weight  of  steam 
in  the  cylinder  between  the  points  of  cut-off  and  lelease,  and 
between  compression  and  admission,  should  be  constant,  as 
both  the  steam  and  exhaust  valves  are  closed.  It  is  found, 
however,  that  this  is  seldom  the  case,  for  reasons  which  will  now 
te  explained.  When  steam  first  enters  the  cylinder  through  a 
port  which  has  just  been  cooled  by  the  exhaust  steam  of  the 
previous  stroke,  some  of  it  is  condensed.  The  point  of  cut-off 
is  reached,  therefore,  with  a  mixture  of  steam  and  water  in  the 
cylinder.  After  cut-off  occurs  expansion  begins,  and  as  the 
pressure  decreases  the  loiling-point  is  lowered.  The  water 
which  was  condensed  early  in  the  stroke  begins  to  evaporate,  and 
by  the  time  release  takes  place  a  considerable  amount  of  water 
has  been  re-evaporated,  though  never  all  of  it.  It  is  evident  that 
there  will  usually  be  more  steam  in  the  cylinders  at  release  than 
at  cut-off  though  the  weight  of  the  steam  and  water  will  be  the 
szme.  From  the  above  it  is  also  evident  that  the  indicator- 
ca:d  will  not  account  for  all  the  water  used  and  that  the  amount 
calculated  from  it  will  always  be  less  than  the  actual  amount. 
The  steam  which  is  caught  in  the  cylinder  at  the  point  of  com- 
pression mixes  with  the  entering  steam  on  the  next  stroke,, 
hence  the  weight  of  steam  and  water  in  the  cylinder  during 
expansion  is  in  excess  of  the  weight  which  enters  per  stroke  by 
the  weight  during  compression. 

Finding  th?  weight  of  steam  per  stroke,  therefore,  is  simply 
a  matter  of  finding  the  weight  at  release  and  subtracting  from 
it  the  weight  at  compression. 


INDICATORS. 


189 


To  find  the  weight  at  release,  erect  an  ordinate  (Fig.  162)  at 
any  point  /  on  the  expansion  line  near  release.  By  measuring 
the  card  find  the  per  cent  of  the  stroke  represented  by  this 
point  and  add  the  clearance  in  per  cent  to  it.  This,  multiplied 
by  the  piston  displacement,  will  give  the  volune  of  steam  behind 
the  piston.  Having  found  the  volume  its  weight  is  found  as 
follows:  Find  the  pressure  of  the  steam  by  measuring  the  ordi- 
nate hj  and  multiplying  by  the  scale  of  the  indicator-spring. 


FIG.  162. 

For  the  pressure  thus  found,  the  weight  of  a  cubic  foot  of 
steam  is  found  in  column  9  of  the  steam  tables.  This,  multi- 
plied by  the  volume  in  cubic  feet,  gives  the  weight  at  release. 
To  determine  the  weight  at  comp  ess  ion  select  some  point  g  on 
the  compression-curve  and  proceed  as  atove. 

Let  W ',  be  the  weight  of  steam  at  release  on  H.E. 

wt  "     "        "       "       "      "  compression  on  H.E. 

Wtl  "     "       "       "       "       "  release  on  C.E. 

w.t  "     "  "       "       "  compression  on  C.E. 

Then          W ',  -w,  =W'  =  weight  of  steam  per  H.E.  stroke 
and  Wll-wll=w'^      "      "      "        "C.E.       " 

Weight  of  steam  per  revolution  =W ' +  w'  and  per  H.P.  per 

(JF'+w')XR.P. 
hour,  -  Hp 


190 


STEAM-POWER. 


To  Construct  the  Theoretical  Expansion-line. 

Expansion  of  steam  in  a  cylinder  is  the  result  of  shutting  off 
the  steam-supply  before  the  end  of  the  stroke.  In  some  early 
engines  live  steam  was  admitted  during  the  whole  stroke. 
Suppose  for  instance  that  steam  is  passing  into  a  cylinder  at 
full  pressure  until  the  middle  of  the  stroke  is  reached;  we  then 
have  a  half  cylinder  full  of  steam  which,  during  the  remainder 
of  the  stroke,  expands  according  to  Mariotte's  law,  the  pres- 
sure varying  inversely  as  the  volume.  The  curve  representing 
this  variation  in  the  pressure  is  a  hyperbola. 

Let  Fig.  163  represent  an  indicator-card.  It  is  desired  to 
find  how  nearly  it  comes  to  ideal  conditions  of  expansion. 


FIG.  163. 

First  it  is  necessary  to  find  the  ratio  of  the  clearance  to  the 
volume  swept  over  by  the  piston.  Take  any  two  points  a  anc 
b  on  the  compression-line  and  on  them  erect  the  rectangle 
acbd.  Draw  the  vacuum-line.  This  is  A'B',  parallel  to  AB< 


INDICATORS.  191 

the  atmospheric  line,  and  at  a  distance  below  it  corresponding 

to  atmospheric  pressure;  for  a  4O-lb.  spring  it  would  be  -^- 

40 

inches.      Draw  the  diagonal  dc  meeting  A'B'  at  O,  which  will 
be  the  origin  of  the  hyperbola  of  expansion .     To  construct  the 


1    3    7 


\ 


DOTTED  LINE  6  -  7,          LATE  AD. 
DOTTED  LINE  8  -  9  »      RELEASE 

DOTTED  UNE  3-4-5,  TOO  GREAT  EXPANSION 
FULL  LINE  NORMAL 


9  S 


FIG.  164/3. 


DOTTED  LINE  3  -  4,          EARLY  RELEASE 
DOTTED  LINE  «  -  8,          WIRE  DRAWING 
DOTTED  UNE  5-6-7,  TOO  GREAT  COMPRESSION 
FULL  LINE  NORMAL 


FIG.  1643. 

theoretical  expansion-curve  take  any  point  m  on  the  expansion- 
line  of  the  card,  after  the  cut-off,  and  draw  mn  perpendicular 
toAB. 

Through  ;;/  also  draw  a  line  ml  parallel  to  AB.  Draw  Ol 
cutting  mn  at  P  and  ml  at  /.  On  the  points  P  and  /  construct 
a  rectangle.  The  point  E  will  be  a  required  point  on  the 
curve.  Any  number  of  points  may  be  found  in  the  same 
manner,  and  the  curve  filled  in  as  shown.  In  this  example, 


TQ2  STEAM-POWER. 

it  is  seen  that  the  actual  expansion-line  falls  below  the 
theoretical  line,  indicating  a  considerable  loss  of  some  kind. 

The  compression-line  may  be  determined  in  the  same 
manner. 

Indicators  are  also  used  in  determining  the  conditions  of 
working  and  work  done  in  the  cylinders  of  Gas-engines,  Air- 
engines,  Air-compressors,  Water-engines,  etc. 

EFFICIENCY. 

The  efficiency  of  any  machine  is  the  ratio  of  the  energy  it 
converts  into  work  to  the  energy  supplied. 

In  the  steam-engine,  efficiency  may  be  of  two  kinds,  thermal 
and  mechanical.  In  consideration  of  the  former,  the  cylinder 
has  fed  to  it  a  certain  quantity  of  steam.  This  steam  has  in 
it  a  determinate  quantity  of  heat,  which  represents  the  supplied 
energy.  The  energy  converted  into  work  may  be  found  by 
testi-g  the  engine,  using  an  indicator,  thus  determining  the  cyl- 
inder horse-power.  By  reducing  these  to  the  same  units  of 
eneigy,  and  dividi  g  the  latter  by  the  former,  we  get  thermal 
efficiency. 

As  an  example,  take  an  enghe  which  develops  ico  H.P., 
and  uses  36,000  pounds  of  stean  in  12  hours.  The  steam  has 
a  pressure  of  100  pounds  absolute  and  2%  moisture.  The 
feed- water  has  a  temperature  of  90°  F.  It  is  required  to  find 
the  thermal  efficiency. 

One  pourd  of  steam  at  100  pounds  absolute,  and  2% 
moisture,  has  in  it  1164  14  B.T.U.  A  pcu  d  of  water  at  90°  F. 
has  in  it  58.06  B.T.U.  The  heat  supplied  to  the  engine  per 
pound  of  steam  is,  therefore,  1164.14-58.06  =  1106.08  B.T.U. 
The  mechanical  equivalent  of  the  heat  suppli  d  per  minute,  in 

110608x36000x778 
fcot-pounds,  is  —     ^—^ -  =  43,026,512.       The  work 

1 2  X  OO 

done  in  foot-pounds  is  100X33,000=3,300,000.      The  thermal 
efficiency  is,  therefore,  3,300,000  •*-  43,026,5  2  =  .076  =  7.6%. 
Other   more   common   methods   of   expressirg    the  thermal 


INDICATORS.  193 

efficiency  are  "pounds  of  st:am  per  indicated  horse-power  per 
hour,"  and  "B.T.U.  p:r  indicated  horsepower  per  minute." 
"Pounds  of  steam  per  I.H.P.  p:r  hour,"  in  the  above  ex- 


ample, would  be  --—    -  =  30,   and    "B.T.U.    per   I.H.P.   per 

1  2  X  IOO 

minute"  would  be  —  -  =  829.56.      The   former   is 

o  X  oo  X  i  oo 

an  approximate  measure  o;ly,  of  the  thermal  efficiency,  as  it 
does  not  take  into  account  the  temperature  of  the  feed-  water 
and  steam.  The  litter  is  an  exact  measure  of  the  efficiency 
and  varies  inversely  with  the  same. 

Pounds  of  steam  per  horse-power  per  hour  is  often  called 
the  commercial  efficiency. 

The  following  is  given  to  acquaint  the  student  with  the 
actual  performance  cf  the  more  common  types  of  engines: 

Maximum  ......  9.56  pounds  of  steam  per  I.H.P.  per  hour. 

Corliss  .........  20  "  "  "  "  "  "  " 

Locomotives....  35  "  "  "  "  "  "  " 

Slide-valve  .....  40  "  "  "  "  "  "  " 

Small  pumps.  ..  200  "  "  "  "  "  "  " 
Steam  turbines 

(large)..  13  "  "  "  "  "  "  " 

• 
Mecbarical  efficie'cy  is   the  ratio   of  the  power  developed   at 

the  crank-shcft  to  trnt  at  the  cylinder,  or  the  latio  of  the  brake 
ho  se-powe  to  ti:e  indicated  horse-power.  It  vaiies  from  0.75 
to  0.94. 

PROBLEMS. 

1.  Trace  the  cards  given  in  Fig.  162  and  locate  admission,  cut-off, 
release,  and  compression  for  H.E.  and  C.E.   cards.      Draw  in   also, 
the   clearance,   boiler-pressure,  and  vacuum   lines.      Barometer  14.5 
pounds;  boiler  pressure  105  pounds,  gauge;   clearance,  head  end  8%, 
crank  end  9%;  spring  80. 

2.  In  the  above  problem,  measure  all  per  cents  and  pressures  and 


194 


STEAM  POWER. 


place  the  results  on  the  cards.     Dei ei mine  also  the  mean   effective 
pressure  for  both  cards. 

3.  If    the    above    cards    were    taken    from    a    i2"Xi6"     engine 
making  188  R.P.M.   (piston  rod  2   inches),  what  horse-power  was  it 
developing? 

4.  An    engine    15"  ¥22''  has  a  piston  rod  3  inches    in    diameter. 
The   clearance,    on    head   end,    is    11%    and    on    crank    end    11.5%. 
During  a  test  the  following  cata  was  taken:    R.P.M.  85,  steam  pres- 
sure,  by  gauge,  100  pounds;  barometer,  14.5  pounds;  moisture.  2%; 
weight  of  steam  used   per   hour,  3000   pounds;    temperature   cf  feed 
water,  84°  F.     From  indicator  cares  the  following  cata  was  determined 
as  in  Prcblems  i  and  2: 

Area      of  H.E.  card,  4.54  square  inches. 

"  C.E.  "      465 

Length  "  H.E.  "       4.26  inches. 

"  C.E.  "      4-25      " 


Events. 

Pressure 

Absolute. 

Per  Ctnt 

of  Stroke. 

H.E. 

C.E 

H.E. 

C.E. 

Cu  -off 

IOI    ^ 

10^  ^ 

AO. 

•JQ  2  C 

Release       

48  ; 

CQ  s 

04 

06 

Compression     

16  <; 

17 

2O  Z 

2O  7C 

^.ca.e  of  spring,  60. 

5.  From  the  <fata  given,  find  the  heat-units  added  to  each  pound 
of  steam  supplied  to  the  engine.     Calculate  the  engine  constant,  H.E. 
and  C.E.,  also  the  displacement  H.E.  and  C.E. 

6.  Calculate  the  volume  behind  the  piston  at  cut-off,  release  and 
compression  fcr  H.E.  and  C.E. 

7.  Calculate  the  weight  of  steam  at  cut-off,  release,  and  compression 
for  H.E.  and  C.E.,  using  the  volumes  obtained  in  Problem  6. 

8.  Calculate  the  horse-power,  H.E.,  and  C.E. 

9.  Calculate  the  actual  number  of  pounds  of  steam  per  H.P.  per 
hour. 

10.  Calculate  the  actual  number  of  B.T.U.  per  I. H.P.  per  minute. 

11.  Calculate  the  number  of  pounds  of  steam  per  I.H.P.  per  hour 
by  indicator. 


INDICATORS.  195 

12.  Calculate  the  percentage  weight  of  steam  per  H.P.  per  hour 
unaccounted  for  by  the  indicator  cards. 

13.  A  card  taken  from  the  H.E.  of  an  engine  gives  the  following 
data:  Initial  pressure,   120.3  pounds  gauge;  barometer,  14.7  pounds; 
clearance,  8%;  cut-off,  30%;  release,  84%.    Find  the  absolute  pressure 
at  release  and  at  60%  of  the  stroke,  also  the  terminal  pressure.      See 
Marriotte's  law. 

14.  An  engine  developing  200  H.P.  uses  5000  pounds  of  steam  per 
hour.    In  each  pound  of  steam  supplied  to  it,  there  are  1120  B.T.U. 
Find  B.T.U.  per.  I. H.P.  per  minute. 

15.  Find  the  thermal  efficiency  of  an  engine  to  which  410  B.T.U. 
are  supplied  per  I. H.P.  per  minute. 

1 6.  If  the  clearance  on  the  H.E.  is  5%  and  the  cut-off  occurs  at 
21%,  what  is  the  total  number  of  expansions? 


CHAPTER    XVIII. 
COMPOUND    ENGINES. 

IN  the  Simple  Engine  the  steam  after  cut-off  expands  until 
the  release-point  is  reached.  The  degree  of  expansion  depends 
upon  the  point  of  cut-off.  The  earlier  the  point  of  cut-off  the 
greater  the  expansion  and  vice  versa.  By  making  cut-off  very 
early  or  by  connecting  a  condenser,  the  steam  may  be 
expanded  until  its  pressure  becomes  less  than  atmospheric 
pressure  (see  Fig.  1640).  The  steam,  after  expansion  has 
ceased,  is  exhausted.  Here  the  whole  process  of  expansion 
has  been  accomplished  in  one  cylinder.  Now  this  process  of 
expansion  is  sometimes  carried  on  by  means  of  two  cylinders 
or  more  instead  of  in  one.  That  is,  the  steam  enters  one 
cylinder  and  is  expanded  a  certain  amount,  after  which  it  is 
exhausted  into  another,  in  which  the  expansion  continues. 
This  is  called  compounding,  and  any  engine  in  which  the 
steam  passes  through  two  or  more  cylinders  consecutively  is 
called  a  Multiple-expansion  Engine.  The  term  compound 
is  commonly  used  to  designate  those  engines  in  which  the 
expansion  is  accomplished  in  two  cylinders. 

In  a  compound  engine  the  steam  at  boiler-pressure  enters 
a  comparatively  small  cylinder  called  the  high-pressure  cylin- 
der. It  is  exhausted  into  a  larger  one  called  the  low-pressure 
cylinder.  If  there  are  three  cylinders,  with  three  stages  of 
expansion,  the  last  entered  by  the  steam  is  the  low-pressure 
cylinder,  and  the  one  between  the  high  pressure  and  low 
pressure  is  called  the  intermediate  cylinder.  If  there  are  four 

196 


COMPOUND  ENGINES.  19? 

cylinders,  with  four  stages  of  expansion,  the  one  next  to  the 
high-pressure  cylinder  is  called  the  first  intermediate  and  the 
one  next  to  the  low-pressure  cylinder  is  called  the  second 
intermediate. 

An  engine  in  which  the  steam  exhausted  from  the  first,  or 
high-pressure,  cylinder  passes  into  two  other  cylinders,  half 
into  each,  is  called  a  three-cylinder  compound  engine,  and  an 
engine  with  four  cylinders,  in  which  the  steam  exhausting  from 
the  second,  or  intermediate,  cylinder  passes  into  two  cylinders, 
is  called  a  four-cylinder  triple-expansion  engine. 

Of  the  compound  engine  there  are  two  types,  viz. :  the 
Tandem  and  the  Cross-compound.  Those  in  which  the  cylin- 
ders are  placed  end  to  end  and  having  only  one  piston-rod,  as 
in  Fig.  165,  are  Tandem  Engines  and  those  having  their 
cylinders  side  by  side  and  two  piston-rods  are  Cross-com- 
pounds, Fig.  1 66. 

In  the  tandem  shown  in  the  figure  the  steam  from  the 
boiler  is  entering  the  smaller  or  high-pressure  cylinder  to  the 
left  of  the  piston  and  driving  it  to  the  right. 

The  exhaust  is  leaving  the  right-hand  end  of  the  h.p. 
cylinder  through  the  large  pipe  at  the  bottom  and  entering  the 
l.p.  cylinder  at  the  left  of  the  piston.  It  will  be  noticed  here 
that  this  pressure  of  steam  against  the  low-pressure  piston  is 
also  back-pressure  against  the  h.p.  piston,  but  owing  to  the 
greater  area  of  the  l.p.  piston  a  working  effect  is  produced. 
The  steam-distribution  in  a  cross-compound  engine  is  prac- 
tically the  same  as  the  process  just  described  for  the  tandem 
compound. 

The  tandem  compound  has  only  one  piston-rod  to  which 
both  pistons  are  attached.  This  rod  may  be  made  in  two  sizes 
as  shown  in  cut.  The  tandem  is  much  simpler  than  the  cross- 
compound  by  reason  of  the  fact  that  it  is  practically  a  single 
engine,  having  two  cylinders  and  two  pistons.  This  makes 
its  cost  small  and  it  requires  a  small  floor-space. 

The  cross-compound  has  two  piston-rods,  and  in  fact,  is 
practically  two  separate  engines  operating  one  crank-shaft. 


i93 


STEAM-POWER. 


Simple  and  Compound  Engines  Compared. 


The  object  of  a  compound  engine  is  to  economize  in  the 
use  of  steam.  The  question  may  be  asked:  Is  it  better  to 
make  a  given  number  of  steam-expansions  in  two  cylinders 
rather  than  in  one  ?  The  question  is  answered  by  saying,  in 
some  cases  yes,  in  some,  no. 

It  is  evident  that  by  making  the  point  of  cut-off  early  and 
the  cylinder  large  enough,  any  number  of  expansions  may  be 
made  in  a  single  cylinder,  and  that  compounding  does  not 
necessarily  cause  greater  expansion. 

The  advantage  of  the  compound  is  that  in  some  cases  the 
losses  are  made  less  than  in  the  simple  engine.  The  losses  to- 
which  all  engines  are  subject  are,  principally:  loss  of  heat  by 
radiation,  heating  the  walls  of  the  cylinder,  and  the  loss  due 
to  condensation  of  the  entering  steam  by  the  comparatively 
cool  cylinder-walls,  besides  the  losses  due  to  friction  (mechan- 
ical losses). 

The  loss  due  to  radiation  may  be  reduced  by  covering  or 
lagging,  and  this  may  be  done  equally  as  well  with  the  simple 
engine  as  with  the  compound  engine,  so  that  there  is  no  advan- 
tage to  be  claimed  for  the  compound  in  that  respect. 

The  loss  of  heat  due  to  heating  the  walls  of  the  cylinder 
may  be  reduced  by  giving  the  piston  a  high  speed,  thereby 
shortening  the  period  of  contact  of  each  particle  of  steam. 
Here  again  the  compound  engine  has  no  advantage,  since  the 
simple  engine  is,  in  fact,  more  easily  run  at  high  speeds. 

,  The  losses  of  condensation,  caused  by  the  cooling  of  the 
entering  steam,  however,  are  in  some  cases  made  less  by 
expanding  in  the  two  cylinders  of  a  compound  engine  rather 
than  in  the  single  cylinder  of  a  simple  engine.  The  following 
is  an  explanation:  When  a  certain  number  of  expansions,  say 
eight,  take  place  in  one  large  cylinder  the  steam  at  a  tempera- 
ture a  little  less  than  that  of  the  boiler  enters  the  cylinder  and 
drives  the  piston  forward  at  full  pressure  and  heats  that  end  of 
the  cylinder  up  to  its  own  temperature.  The  cut-off  occurs  at 


COMPOUND  ENGINES.  199 

one  eighth  stroke,  after  which  the  expansion  of  steam  begins 
and  the  temperature  is  correspondingly  decreased  until  the  end 
of  the  stroke  is  reached.  This  action  leaves  the  temperature 
of  the  cylinder-metal  much  lower  at  the  end  of  the  stroke  than 
at  the  beginning.  This  difference  of  temperatures  is  called  the 
range  of  temperature. 

The  steam  on  entering  for  the  return  stroke  gives  up  a 
large  quantity  of  heat  in  warming  the  cool  end  of  the  cylinder 
up  to  its  temperature,  and  so  for  every  stroke  there  is  an 
alternate  cooling  and  warming,  very  detrimental  to  economy. 

By  making  the  eight  expansions  take  place  in  two  cylin- 
ders, with  cut-off  say  at  one  half  stroke  in  the  high-pressure 
cylinder,  making  two  expansions,  and  then  exhausting  into  a 
low-pressure  cylinder  with  a  volume  four  times  as  large  as  the 
high-pressure  cylinder,  making  a  total  of  eight  expansions,  the 
range  of  temperature  in  each  cylinder  is  reduced.  This  is  the 
principal  advantage  of  the  compound  engine.  Another  advan- 
tage is  that  by  the  use  of  two  cylinders  for  expansion,  and  a 
given  pressure  for  the  exhaust,  much  higher  initial  pressures 
of  steam  may  be  used.  It  is  known  to  be  economical  to  use 
steam  at  very  high  pressures  and  temperatures,  because  the 
cost  of  obtaining  very  high  pressures  in  a  boiler  is  compara- 
tively very  small  after  a  moderately  high  pressure  is  once 
attained.  This  is  accounted  for  by  the  fact  that  the  greater 
part  of  the  heat  at  low  pressures  is  spent  in  breaking  up  the 
molecular  construction  of  the  water,  while  it  is  comparatively 
easy  to  increase  the  pressure  of  the  steam  after  it  has  once 
become  a  perfect  gas. 

Another  advantage  of  the  compound  engine  is  that  the 
effort  may  be  distributed  at  different  angles  on  the  crank-shaft, 
if  a  cross-compound  is  used.  The  hottest  steam  is  used  in  the 
cylinder  of  the  smallest  volume.  This  causes  a  diminution  of 
the  loss  due  to  radiation. 

There  are  objections  to  the  compounding  principle,  such 
as  increase  in  first  cost,  the  friction  is  increased  by  reason  of 
the  increased  number  of  moving  parts,  especially  in  the  cross- 


200  STEAM-POWER. 

compound,  the  greater  loss  of  radiation  from  two  cylinders 
instead  of  one,  and  the  fact  that  the  engine  is  wasteful  of  steam 
as  compared  with  the  simple  engine,  unless  nearly  the  average 
load  for  which  it  was  designed  is  carried. 

Ratio  of  Cylinders. — It  has  been  shown  that  the  low- 
pressure  cylinder  is  of  much  larger  volume' than  the  high-pres- 
sure cylinder.  Since  the  volume  of  a  cylinder  varies  as  the 
square  of  the  diameter,  if  R  be  the  ratio  of  the  volume  of  the 
high-pressure  cylinder  to  the  volume  of  the  low-pressure 

D* 

cylinder,  then  R  =  -^-,  D  and  d  being  the  diameters  respec- 
tively of  the  low-pressure  and  high-pressure  cylinders. 

The  value  of  R  depends  upon  the  make  and  type  of  the 
engine  and  is  usually  from  2\  to  4^. 

The  total  number  of  expansions  in  a  compound  engine  is 
equal  to  the  number  of  expansions  in  the  high-pressure  cylinder 
multiplied  by  R. 

Receiver. — It  has  been  explained  that  in  a  tandem  com- 
pound engine,  the  steam-pressure  acts  against  the  same  side 
of  the  high- pressure  and  low-pressure  pistons  at  the  same 
time.  This,  however,  is  not  the  case  with  the  cross-compound, 
because  the  cranks  are  usually  placed  on  the  shaft  at  an  angle 
of  90°.  Here  the  exhaust  steam  from  the  first  cylinder  cannot 
be  used  directly  in  the  low-pressure  cylinder. 

The  exhaust  from  the  high-pressure  cylinder  is  therefore 
passed  into  an  intervening  vessel,  called  a  receiver,  where  it 
remains  during  a  half  stroke  or  while  the  crank  makes  a  turn 
of  90°. 

The  space  between  the  exhaust-port  of  the  h.p.  cylinder 
and  the  steam-port  of  the  l.p.  cylinder,  in  either  a  tandem  or 
a  cross-compound,  is  -called  receiver- space.  It  includes  the 
exhaust-pipe  of  the  h.p.  cylinder  and  the  steam-chest  of  the 
l.p.  cylinder.  This  space  should  be  as  large  as  possible  in 
order  to  make  frictional  resistance  of  the  steam  small. 

The  expansion  of  the  steam  in  the  h.p.  cylinder  is  attended 
with  a  lowering  of  the  temperature.  For  the  purpose  of 


COMPOUND  ENGINES. 


201 


reheating"  this  steam,  some  manufacturers  have  introduced  a 
coil  of  pipe  carrying  hot  steam  from  the  boiler  into  this 
receiver-space  between  the  two  cylinders. 

Indicator-cards. — In  order  to  get  an  indicator-card  from 
the   two   cylinders   of  a  compound   engine  it  is  necessary  to 
attach  an  indicator  to  each  cylinder  and  connect  them  indi- 
vidually or  by  the  same  string  to  the  reducing  motion. 
H  G 

A 


F  d  E 

FIG.  1670. — Indicator-card  taken  from  Compound  Engine. 


FIG.  167^. — Card  from  High-pressure  Cylinder. 

In  Fig.  167  (a)  is  a  card  taken  from  the  h.p.  cylinder  and 
(£)  one  taken  from  the  low-pressure  cylinder  of  a  compound 
engine.  The  length  of  the  engine-stroke  is  represented  by 


OF   TH* 

UNIVERSITY 


^c  2  5  TEAM-PO  \VER. 

FE,  and  boiler-pressure  by  FH.  FE  is  the  atmospheric  line. 
AB  is  the  steam-line,  and  B  is  the  point  of  cut-off  for  the  h.p. 
cylinder.  As  the  piston  advances  the  volume  of  .steam  in  the 
h.p.  cylinder  increases  and  the  pressure  decreases  correspond- 
ingly, producing  BC,  the  high-pressure  expansion -curve. 
The  point  C  represents  the  position  of  the  high-pressure  piston 
when  its  exhaust-valve  is  opened  and  the  steam  allowed  to 
pass  into  the  low-pressure  cylinder. 

This  point  C  also  represents  the  end  of  the  h.p.  piston- 
stroke,  after  which  its  return-stroke  begins,  the  pressure  falling 
to  D  as  the  steam  expands  into  the  l.p.  cylinder.  The  point 
D  is  the  point  of  compression  for  the  h.p.  cylinder,  that  is, 
when  the  valve  which  opens  at  C  closes.  DJ\s  the  compres- 
sion-curve, and  ythe  point  of  admission  of  the  h.p.  cylinder. 

Let  us  now  turn  our  attention  to  the  low-pressure  card. 
The  same  edge  of  the  valve  which  exhausts  the  steam  from 
the  h.p.  cylinder  admits  it  to  the  low-pressure  cylinder,  hence 
C  is  the  point  of  admission  for  the  l.p..  cylinder.  Also,  since 
the  h.p.  exhaust  is  the  l.p.  steam,  the  line  CD  for  the  two 
cylinders  should  be  -common.  If  there  is  a  space  between 
them,  it  is  caused  by  frictional  losses. 

PROBLEM. 

T.  Find  the  H.P.  of  the  compound  engine  from  which  the  card 
in  Fig.  1670  was  taken,  the  stroke  of  both  pistons  being  12  inches,  the 
diameter  of  the  high-pressure  piston  8  inches,  and  the  diameter  of  the 
low-pressure  piston  12  inches,  piston-rods  i%  inches,  and  the  number 
of  revolutions  per  minute  150.  Number  of  spring,  60. 

To  Combine  the  Indicator-cards  of  a  Compound  Engine. 
— Let  Figs.  167^  and  \6jc  represent  average  cards  from  a 
compound  engine,  obtained  by  averaging  the  cards  from  the 
head  and  crank  end  of  each  cylinder.  Divide  each  card  into, 
say,  ten  equal  parts,  and  erect  ordinates  at  the  points  of  division. 
Now  take  a  line  AB,  Fig.  167^,  as  an  atmospheric  line,  and 
CD  as  a  line  of  zero  volume.  Select  on  AB  some  convenient 
distance,  as  EF,  for  the  length  of  the  high-pressure  card  on  the 


COMPOUND  ENGINES.  2C3 


combined  diagram.  Divide  this  distance  into  the  same  number 
of  equal  parts  as  the  h.p.  card  and  erect  ordinates.  The 
clearance  of  the  high-pressure  cylinder  being  known,  lay  off 
the  distance  GH  to  represent  the  clearance.  GH  should  be 


FIG.  167*:.  —  Card  from  Low-pressure  Cylinder. 

the  same  percentage  of  EF  as  the  clearance  is  of  the  volume 
of  the  cylinder.  Then  enlarge*  the  ordinates  on  the  high- 
pressure  card,  Fig.  167^,  to  a  convenient  scale  and  take  the 
ordinates  erected  in  Fig.  i6/*/as  equal  to  the  length  found  by 
this  enlargement.  Draw  a  curve  through  the  extremities  of 
the  ordinates.  This  curve  will  be  the  high-pressure  card  on 
the  combined  diagram. 

Now  let  the  volumes  of  the  high-  and  low-pressure  cylin- 

V 

ders,  swept  over  by  the  piston,  be  to  each  other  as  -=^  .    Then 

*i 
the   length   JK  of  the   low-pressure   card    on    the    combined 

diagram  will  be 


Lay  off  the  distance  G  K  as  the  clearance  of  the  low-pressure 
cylinder,  GK  being  the  same  proportion  of  JK  as  the  clearance 
of  the  low-pressure  cylinder  is  of  its  volume. 

Then  erect  the  same  number  of  ordinates  on  the  atmos- 
pheric line   as  were   erected   on   the   low-pressure   card,   Fig. 

*  Multiply. 


2O4 


STEAM  POWER. 


\6jc.  Determine  the  length  of  these  ordinates  by  enlarging 
or  reducing  those  on  the  original  low-pressure  card  to  the  same 
scale  as  the  high-pressure  ordinates  on  the  combined  card,  and 
taking  their  length  as  the  length  of  the  ordinates  on  the  com- 


bined  card.  Draw  the  card  through  the  ext  ities  of  these 
ordinates;  draw  DL,  the  line  of  zero  absolute  pressure,  and 
MN,  the  line  of  back  pressure. 


COMPOUND  ENGINES.  205 

Now  if  the  actual  area  of  the  combined  indicator-cards  be 
compared  with  the  theoretical  area  for  the  volume  of  steam  at 
boiler-pressure  admitted  to  the  high-pressure  cylinder  expand- 
ing to  the  volume  in  the  low-pressure  cylinder,  the  back  pres- 
sure being  taken  as  that  in  the  condenser,  the  ratio  of  the  area 
of  the  cards  to  the  theoretical  area  is  the  ratio  of  the  work 
done  in  the  cylinder  to  the  theoretical  work. 

The  theoretical  area  is  determined  by  extending  the  com- 
pression-curve according  to  the  law  pv  =  constant  until  it 
meets  the  line  of  boiler-pressure  at  O,  and  also  the  expansion- 
line  from  some  point  below  the  cut-off  until  it  meets  the  boiler- 
pressure  line  at  P.  Make  QR  equal  to  OP  and  draw  Martotte's 
curve  RS,  taking  T  as  the  origin.  Lay  off  the  distance  TV, 
making  it  equal  to  JK,  the  length  of  the  low-pressure  card. 
Erect  the  ordinate  VU.  The  actual  areas  and  the  theoretical 
area  are  found  by  planimeter;  the  theoretical  area  is  QRUVTQ. 

It  is  assumed  in  this  case  that  the  length  of  stroke  and 
number  of  revolutions  is  the  same  for  each  cylinder 


CHAPTER    XIX. 


CONDENSERS. 

THE  condenser  is  frequently  used  with  the  simple  engine, 
but  the  common  practice  is  to  make  compound  or  multiple- 
expansion  engines  condensing.  The  object  of  the  condenser 
is  to  economize  in  the  use  of  steam,  or,  in  other  words,  to  get 
more  nearly  the  entire  ene  gyfrom  the  steam  in  an  engine  than 
could  be  obtained  without  one. 

The  steam  from  an  engine  if  exhausted  into  the  atmosphere 
causes  a  small  back  pressure  on  the  side  of  the  piston  opposite 
the  live  steam.  Making  the  exhaust-pipe  discharge  vertically, 
making  it  very  long,  or  causing  it  to  make  sharp  turns,  all  tend 
to  increase  this  back  pressure. 
For  illustration  let  A  and  B 
in  Fig.  1 68  represent  a  cylinder 
and  piston.  The  live  steam  is 
entering  and  pushing  the  piston 
towards  the  right.  Suppose  that 
b  opens  to  the  atmosphere,  then 
the  pressure  on  the  side  C  will 
be  14.7  pounds  plus  that  due 
to  the  friction  of  the  steam  in 
the  exhaust-pipe  and  to  inertia. 
This  is  a  real  loss  because  it 
neutralizes  just  that  much  of 
the  pressure  of  the  live  steam 
on  the  side  A. 

Suppose,  however,  that  b  is  made  to  open  into  a  chamber 
D,  and  that  by  a  spray  of  water  or  otherwise  the  steam  is  con- 

206 


FIG.  168. 


CONDENSERS.  207 

Sensed  immediately  upon  entering.  By  this  means  the  entire 
volume  of  steam  is  reduced  to  a  few  drops  of  water  in  the 
bottom  of  D.  It  is  evident  that  this  will  produce  a  partial 
vacuum  in  D.  This  changes  the  back  pressure  to  an  effective 
forward  pressure.  This  partial  vacuum  is  usually  made  still 
more  perfect  by  means  of  an  air-pump  which  draws  not  only 
the  air  from  D  but  keeps  it  free  from  water. 

The  foregoing  is  merely  to  illustrate  the  principle  of  the 
condenser.  The  principal  difference  in  the  different  makes  of 
condensers  is  in  the  manner  of  cooling  the  exhaust  steam. 
This  is  done  either  by  bringing  it  in  direct  contact  with  a 
jet  or  spray  of  water,  or  by  bringing  it  in  contact  with  tubes 
which  are  kept  cool  by  circulating  water  through  them.  The 
former  is  called  the  Jet-condenser,  the  latter  the  Surface-con- 
denser. 

The  Jet-condenser. — In  a  jet-condenser  the  exhaust  steam 
from  the  engine  enters  a  chamber  called  the  condensing- 
chamber,  where  it  is  intercepted  by  a  spray  of  cold  water  and 
condensed ;  it  then  falls  with  the  condensing  water  to  the 
bottom  of  the  condensing-chamber.  From  here  it  is  drawn 
off,  usually  by  an  air-pump,  to  a  reservoir  called  the  hot-well. 
From  the  hot-well  it  is  taken  as  it  is  needed  to  the  boiler  by 
the  feed-pump,  providing  it  has  been  previously  freed  from  oil, 
by  means  of  a  separator  or  filter. 

Fig.  169  is  an  illustration  of  this  type.  It  is  made  by  the 
Worthington  Hydraulic  Works.  The  exhaust  steam  from  the 
engine  enters  at  A.  F is  the  condensing-chamber  into  which 
the  condensing-water  is  introduced  at  B  and  through  D  which 
sprays  it.  The  condensed  steam  falls  to  the  bottom  and  is 
forced  out  through  J  by  the  air-piston  G.  This  air-piston  is 
worked  by  the  steam-engine  at  K.  The  water  is  carried  from 
J  to  the  hot-well.  The  amount  of  condensing-water  admitted 
is  controlled  by  means  of  the  hand-wheel  E. 

The  principal  parts  of  a  jet-condenser  are  the  condens- 
ing-chamber, the  air-pump,  and  the  hot-well. 

Surface-condenser. — In  the  surface-condenser  the  exhaust 


208 


STEAM-POWER. 


steam  from  the  engine  enters  a  condensing-chamber,  which 
consists  of  a  vessel  in  which  a  number  of  tubes  are  placed, 
with  water  circulating  through  them.  The  hot  steam  is  cooled 


FIG.  169. — Jet-condenser. 

and  condensed  on  coming  in  contact  with  the  cool  pipes.  It 
falls  to  the  bottom  of  the  condensing-chamber,  as  in  the  jet- 
condenser,  and  is  drawn  off  to  the  hot-well  by  the  air-pump. 

Fig.   170  shows  in  section  a  condenser  of  this  type  made 
by  the  Wheeler   Condenser  and  Engineering  Co.      The  ex- 


CONDENSERS. 


209 


haust  steam  enters  the  top  of  the  condensing-chamber,  strik- 
ing the  baffle-plate,  which  spreads  it  and   protects  the  tubes 


nearest  the   entering  steam.     The  steam  is   condensed  upon 
striking   the  tubes,  and  falls  to  the  bottom  of  the  condenser, 


210  STEAM-POWER. 

whence  it  is  drawn  off  by  the  air-pump  and,  if  the  oil  in  the 
water  has  been  removed,  is  taken  off  to  the  hot- well  or  to  the 
boiler  through  the  outlet  shown  in  the  figure  by  the  dotted 
circle. 

The. principal  parts  of  the  surface-condenser  are:  The  con- 
densing-chamber,  the  air-pump,  the  hot-well,  and  the  circulat- 
ing-pump, the  same  as  for  the  jet-condenser  with  the  addition 
of  the  circulating-pump.  The  condensing  water  enters  at  the 
bottom,  thus  causing  the  coolest  water  to  meet  the  cooler 
steam  and  vice  versa.  This  reduces  the  damage  done  by 
uneven  expansion  in  the  tubes  and  tube-plates. 

Jet-  and  Surface-condenser  Compared. — From  the  two 
foregoing  examples  it  may  be  seen  that  the  jet-condenser  is 
much  simpler  in  construction  than  the  surface-condenser. 
For  this  reason  the  jet-condenser  is  used  largely  on  land. 
Since  the  cooling  water  comes  in  direct  contact  with  the  steam 
it  is  obvious  that  pure  water  must  be  used  for  cooling  purposes 
if  it  is  used  in  the  boiler  again. 

The  surface-condenser  has  the  advantage  that  its  condens- 
ing water  does  not  come  in  direct  contact  with  the  steam. 
This  makes  it  possible  to  use  any  kind  of  water  for  cooling 
purposes.  Salt  water  at  sea,  muddy  water,  etc.,  may  be  thus 
used.  For  this  reason  the  surface-condenser  is  used  on  sea- 
going vessels,  in  which  case  the  condensing  water  is  salt  and 
it  is  allowed  to  run  back  into  the  sea.  When  surface-con- 
densers are  used  on  land  the  condensing  water,  after  it  has 
accomplished  its  cooling  effect  and  been  heated,  is  usually 
allowed  to  run  to  waste.  Sometimes,  however,  this  water  is 
used  over  again  after  cooling  it  by  some  method.  One  of 
these  methods  is,  to  cause  it  to  run  along  a  series  of  shallow 
troughs  in  the  open  air  exposed  to  the  cooling  effect  of  natural 
winds.  The  troughs  are  arranged  one  over  the  other  with  a 
slight  grade  so  that  the  water  finally  reaches  the  bottom  trough 
cooled,  from  which  it  is  pumped  again  through  the  condenser. 
Another  later  and  better  method  is  to  cause  the  heated  water 
to  descend  in  a  cooling-tower,  in  a  divided  state,  through  trays 


CONDENSERS.  211 

of  wire  gauze.     A  circulating-fan  induces  a  current  of  air  which 
causes  a  vaporization  and  cooling  of  the  water.      When  it  has 


TOWER 


:<     C<56  HOT  WATER. 


COLDWATEH, 


SUCTION   TANK 

FIG.  171. — Cooling-tower. 


fallen  to  the  bottom  of  the  tower  and  become  cool  it  is  again 
pumped  through  the  condenser. 


212 


STEAM-POWER. 


Fig.   171   shows  this  arrangement  used  in  connection  with 
a  jet-condenser. 


One  of  the  principal  objections  to  the  surface-condenser  is 
that  the  expansions  and  contractions  of  the  tubes  caused  by 
their  heating  and  cooling  causes  much  trouble  from  their  leak- 


CONDENSERS. 


213 


214  STEAM-POWER. 

ing,  similar  to  those  in  tubular  boilers.  This  is  generally 
obviated  by  making  the  tubes  fast  to  one  head-plate  and 
movable  with  reference  to  the  other,  a  joint  being  made  in 
the  manner  of  a  stuffing-box.  The  tubes  are  also  liable  to 
be  destroyed  by  corrosion. 

Fig.  173  illustrates  several  ways  of  making  such  a  joint. 
When  the  tube  increases  in  length  by  reason  of  expansion  by 
heating,  this  joint  allows  the  end  to  slide.  Fig.  170  shows  a 
unique  method  of  avoiding  the  difficulty  stated  above.  The 
condensing  water  passes  through  a  set  of  double  pipes,  one 
within  the  other,  the  smaller  one  fastened  to  one  and  the 
larger  one  or  casing  to  the  other  head-plate.  The  water  enters 
the  small  pipe  at  F  and  flows  to  the  end  at  the  left  and  empties 
into  the  larger  pipe  in  which  it  returns  to  G,  from  whence  it 
goes  to  the  outlet  D.  By  this  means  the  small  pipe  may  slide 
within  the  other  and  prevent  the  disastrous  effects  of  contrac- 
tion and  expansion. 

The  Air-pump. 

The  question  is  sometimes  asked  why  should  the  pump 
which  keeps  the  condenser  drained  of  water  be  called  an  air- 
pump. 

In  reality, 'it  does  assist  not  only  in  pumping  water  but  also 
in   maintaining   and   increasing   the   vacuum   which   has   been  • 
partially  made  by  condensation  and  because  it  also  removes 
air  which  has  entered  in  the  steam. 

The  air  pump  is  a  lifting  or  suction-pump,  and  sometimes 
has  its  valve  ii  the  piston. 

The  pump  is  usually  placed  below  the  condensing-  chamber 
in  order  that  the  water  may  enter  it  by  gravity.  The  air-pump 
piston  may  be  driven  by  a  belt  from  the  engine  or  it  may  be 
driven  by  a  separate  engine,  especially  for  the  purpose.  This- 
kind  is  called  the  independent  condenser,  of  which  the  Wheeler 
and  Worthington  condensers  are  examples. 

The  belt-driven  condenser-pump  has  the  advantage  of 
small  first  cost  and  simple  construction,  but  it  is  obvious  that 
the  speed  depends  on  the  speed  of  the  engine  itself;  and  that 


CONDENSERS. 


2I5 


if  belted  directly  to  the  engine,  it  must  be  in  the  plane  of  the 
engine  in  order  to  receive  the  belt-connection,  making  it 
necessary  to  place  it  oftentimes  where  it  is  in  the  way. 

The  independent  condenser  is  of  higher  fifst  cost  and  more 
complicated  in  construction,  but  it  has  the  advantage  of  being 
more  easily  controlled.  It  can  be  started  before  the  engine  is 
started  and  can  be  speeded  up  or  down  according  to  the  needs 
shown  by  the  vacuum-gauge,  which  is  attached  to  the  con- 
densing-chamber. 

Fig.   174  shows  a  vacuum-gauge.      Its  inner  mechanism  is 


FIG.  174. — Vacuum-gauge. 


It  is 


similar   to    that   of  the    common   steam-  or    air-gauge, 
graduated  to  read  "inches  of  mercury." 

It  is  impossible  to  make  a  perfect  vacuum,  and  in  the 
case  of  the  condenser,  26  inches  of  mercury  or  about  13. 
Ibs.  pressure  is  about  the  average  vacuum  produced.  Tl  e 


2l6 


STEAM-POWER. 


FIG.  175. — Bulkley  Condenser. 


CONDENSERS.  217 

perfection    of  the    vacuum  will   of  course    depend    upon    the 
efficiency  of  the  air-pump. 

The  Siphon  Condenser. 

Tne  atmospheric  pressure  will  support  a  column  of  water 
over  32  feet  high.  This  principle  is  sometimes  used  to  make 
a  condensing-plant  without  an  air-pump. 

The  principle  is  applied  by  the  use  of  a  pipe  34  feet  high,, 
at  the  top  of  which  is  placed  an  arrangement  similar  to  art 
injector  through  which  the  exhaust  steam  and  cooling  water 
are  drawn  by  atmospheric  pressure.  Fig.  175  shows  this, 
principle  applied  in  the  Bulkley  Condenser. 

The  exhaust  steam  passes  downward  through  the  goose- 
neck at  the  top  of  the  apparatus  and  through  the  inner  cone- 
surrounded  by  an  annular  cone  of  water.  The  steam  is  con- 
densed here  and  falls  with  the  condensing  water,  entraining  the 
air  as  it  falls.  This  it  will  be  seen  requires  no  air-pump,  but 
the  injection-  or  circulating-pump  is  still  necessary. 

Fig.  176  represents  an  indicator-card  taken  from  the  low- 
pressure  cylinder  of  a  condensing-engine.  Here  it  is  noticeable 


FIG.  176. 

that  the  atmospheric  line,  AB,  is  considerably  above  the  line 
of  counter-pressures,  its  distance  above  the  same  correspond- 
ing approximately  to  the  pressure  due  to  the  vacuum. 

PROBLEMS. 

1.  A  vacuum-gauge  gives  a  reading  of  27  inches.   Find  the  equiva- 
lent pressure  in  pounds  per  square  inch. 

2.  In  the  indicator-card  shown  in  Fig.  176  find  the  approximate 
vacuum  reading    in   inches  of  mercury,    the  scale  of  the    indicator 
being  40. 


CHAPTER    XX. 
VALVES   AND   VALVE-GEARING. 

IN  Chapter  XV  in  the  description  of  the  simple  engine, 
mention  was  made  of  the  fact  that  the  engine  was  operated  by 
a  D  slide-valve.  This  valve  is  shown  in  section  in  Fig.  177, 


.•  FIG.  177. — Slide-valve. 

together  with  a  portion  of  the  valve-seat.  The  spaces  EC 
and  HI  are  the  steam-ports  leading  to  the  cylinder,  EF  is  the 
exhaust-port,  and  DG  is  the  exhaust-chamber  in  the  valve. 
The  portions  of  valve,  AB  and  //,  projecting  beyond  the  out- 
side edge  of  the  ports,  when  the  valve  is  in  its  middle  position, 
are  known  as  the  steam-lap  or  outside  lap  of  the  valve.  The 
portions,  DC  and  HG,  projecting  into  the  exhaust-chamber 
beyond  the  inside  edge  of  the  port  are  the  exhaust-lap  or  inside 

aiS 


VALVES  AND   VALVE-GEARING.  219 

lap  of  the  valve.      The  object  of  these  laps  will  be  explained 
later. 

Lead. — It  has  been  explained  in  Chapter  XV  how  the  valve 
is  moved  by  the  eccentric  so  as  to  admit  steam  to  and  exhaust 
it  from  the  cylinder.  The  manner  in  which  the  valve  is  set 
will  now  be  shown.  Suppose  the  piston  to  be  just  at  the  end 
of  its  stroke.  The  crank-pin  will  be  just  passing  over  the  dead- 
centre,  and  will  be  moving  slower  in  the  direction  of  the  centre 
line  of  the  engine  than  at  any  other  portion  of  the  stroke.  It 
is  desirable  that  steam  be  admitted  to  the  cylinder  as  quickly 
as  possible;  to  do  this  it  is  necessary  that  the  valve  should  be 
moved  quickly,  thus  opening  the  steam-port  wide  in  the 
shortest  possible  time.  If  the  eccentric  is  placed  90°  ahead 
of  the  crank  on  the  crank-shaft,  in  the  direction  of  rotation,  it 
will  be  moving  its  fastest  in  the  direction  of  the  centre  line  of 
the  engine,  at  the  instant  the  crank  is  moving  slowest.  If  the 
eccentric  was  fixed  in  this  position  of  90°  ahead  of  the  crank, 
the  valve  would  be  in  mid-position,  the  centre  line  of  the  valve 
coinciding  with  the  centre  line  of  the  exhaust-port,  when  the 
engine  was  on  its  dead-centre.  Then  before  steam  could  be 
admitted  to,  say,  the  port  HI,  Fig.  177,  the  valve  would  have 
to  move  the  distance  of  the  steam- lap,  //.  But  it  has  been 
stated  that  steam  was  to  be  admitted  as  quickly  as  possible  to 
the  cylinder;  therefore  the  eccentric  is  advanced  still  further 
on  the  crank-shaft,  until  the  point  J  is  just  over  or  beyond  the 
point  /.  The  distance  the  point  J  is  advanced  beyond  /  is 
termed  the  lead  of  the  valve.  The  angle  through  which  the 
eccentric  is  advanced  ahead  of  the  crank  over  90°  is  termed 
the  angle  of  advance.  Thus,  steam  will  enter  the  port  HI  just 
before  the  crank  passes  the  dead-centre,  or  just  before  the 
piston  reaches  the  end  of  the  stroke;  the  amount  of  lead 
determines  how  much  before.  If  the  angle  of  advance  is  such 
that  the  points  J  and  /  coincide  when  the  crank  is  passing  the 
dead-centre,  the  lead  will  be  zero.  The  amount  of  lead  is 
fixed  by  the  angle  of  advance,  and  can  be  altered  by  moving 
the  eccentric. 


220  STEAM-POWER. 

Lap. — The  steam-lap  determines  the  point  of  cut-off  of  the 
engine.  The  greater  the  lap,  the  earlier  the  cut-off  will  occur. 
If  there  were  no  steam-lap  on  the  valve,  that  is,  if  when  the 
valve  was  in  mid-position,  the  point  J and  the  point  /were  to 
coincide,  the  valve  would  admit  steam  during  the  entire  stroke 
of  the  piston.  The  valve  is  wide  open  when  the  eccentric  is 
passing  its  dead-centre.  If  there  is  no  lap  or  lead  the  valve 
will  be  in  mid-position  and  just  closed  when  the  crank  passes 
the  dead-centre,  the  eccentric  being  but  90°  ahead  of  the  crank 
in  this  case.  Now  if  the  valve  be  given  steam-lap  it  is  easily 
seen  that  when  the  valve  is  wide  open,  the  point  J  will  be 
nearer  the  point  /  than  would  be  the  case  if  there  were  no  lap. 
Hence  the  valve  will  close  the  port  before  it  reaches  mid- 
position.  By  making  the  lap  great  enough  it  is  possible  to 
admit  but  a  small  amount  of  steam  to  the  cylinder,  the  cut-off 
occurring  soon  after  the  beginning  of  the  stroke.  The  extreme 
case  is  obtained  if  the  lap  is  made  so  great  that  the  valve  does 
not  open  at  all,  thus  allowing  no  steam  whatever  to  enter  the 
cylinder.  If  such  a  case  were  possible  the  cut-off  would  be 
said  to  occur  at  the  beginning  of  the  stroke. 

The  object  of  the  exhaust-lap  is  to  increase  the  compres- 
sion of  the  steam  in  the  cylinder.  It  acts  in  the  same  manner 
as  the  steam-lap,  closing  the  port  before  the  end  of  the  stroke. 
By  closing  the  port  before  the  end  of  the  stroke  some  steam  is 
trapped  in  the  cylinder,  and  as  it  cannot  get  out  it  is  com- 
pressed by  the  motion  of  the  piston.  In  the  valve  shown  in 
Fig.  177,  if  the  steam  were  compressed  above  the  pressure  of 
the  steam  in  the  steam-chest,  the  valve  might  be  lifted  from 
its  seat.  In  many  cases  therefore  the  valve  is  held  in  place 
by  a  plate  which  presses  against  it  and  is  fastened  to  the  steam- 
chest.  The  valve,  called  in  this  case  a  balanced  valve,  slides 
between  this  plate  and  the  seat. 

The  lap  on  each  end  of  the  valve  is  not  always  the  same. 
If  the  lap,  both  steam  and  exhaust,  were  the  same  the  cut-off 
and  compression  on  each  end  of  the  cylinder  would  be  differ- 
ent. This  is  due  to  the  angularity  of  the  crank.  It  is  usual 


VALVES  AND   VALVE-GEARING.  221 

in  the  design  of  engines  to  equalize  the  cut-off  and  compression 
by  making  the  steam-  and  exhaust-lap  on  the  two  ends  differ- 
ent. The  method  of  equalizing  the  cut-off  and  compression 
will  be  shown  in  the  chapter  on  "  Valve-diagrams." 

Setting  an  Eccentric. — First  put  the  engine  on  a  dead- 
centre.  This  may  be  done  by  bringing  the  piston  almost  to 
the  end  of  the  stroke.  Make  a  mark  on  the  cross-head  and 
another  on  the  guide,  close  beside  the  first  one.  Next  make 
a  mark  on  the  fly-wheel.  This  mark  should  be  opposite  a 
pointer  which  remains  stationary  when  the  engine  revolves. 
When  these  marks  are  all  made,  revolve  the  engine  past  the 
dead-centre,  until  the  mark  on  the  cross-head  is  once  more 
opposite  the  mark  on  the  guide.  Mark  the  fly-wheel  once 
more  opposite  the  pointer.  If  the  middle  point  of  the  arc  on 
the  fly-wheel  between  the  two  marked  points  be  brought 
opposite  the  pointer,  the  engine  will  be  on  the  dead-centre. 
The  eccentric  is  next  brought  90°  ahead  of  the  crank  in  the 
direction  of  rotation  of  the  engine.  Then  it  is  given  an  angle 
of  advance  until  the  desired  lead  is  obtained,  the  steam-chest 
cover  being  removed  to  make  the  valve  visible.  The  eccentric 
should  be  temporarily  fastened  until  the  engine  has  been  put 
on  the  opposite  dead-centre,  and  it  has  been  ascertained  if  the 
leads  on  both  ends  are  equal.  If  they  are  not,  they  should  be 
made  so  by  adjusting  the  length  of  the  valve-rod  and  then  the 
proper  amount  of  lead  is  given  by  turning  the  eccentric  on  the 
shaft  in  a  direction  depending  upon  whether  a  greater  or  a  less 
lead  is  desired. 

If  it  is  desired  to  run  an  engine  in  the  opposite  direction  to 
which  it  is  already  running,  the  eccentric  should  be  loosened 
and  rotated  on  the  shaft  until  it  is  as  much  behind  the  crank 
as  it  was  formerly  ahead  of  it.  The  engine  should  be  put  on 
the  dead-centres  and  the  lead  equalized,  just  as  if  the  valve 
was  being  set  for  the  first  time. 

Reversing  Gears. — There  are  a  number  of  valve-gears  in 
existence,  both  for  reversing  and  for  varying  the  cut-off.  The 
simplest  of  these  is  the  Stephenson  link,  shown  in  Fig.  178. 


222 


STEAM-POWER. 


The  gear  consists  of  the  link  CD,  which  is  connected  with  the 
two  eccentrics  A  and  B  on  the  shaft  5  by  the  eccentric-rods 
CA  and  BD.  A  block  E  slides  in  the  link.  A  rod  EF  joins 
this  block  to  a  rocker  HGF.  The  valve-rod  HI  is  attached  to 
the  other  end  of  the  rocker  which  rotates  about  G.  One 
eccentric  is  the  "  go-ahead  "  eccentric  ;  the  other  is  the  revers- 
ing eccentric.  If  the  rocker  HGF  were  not  interposed,  B 


FIG.  178. — Stephenson  Link. 

would  be  the  forward  eccentric,  but  the  relative  direction  of 
motion  of  the  eccentric  and  valve-rods  is  reversed  by  the 
rocker.  In  the  position  shown  by  the  full  lines,  the  block  is 
at  the  middle  of  the  link;  the  two  eccentrics  neutralize  each 
other  and  the  piston  cannot  move.  To  move  the  engine 
either  way  the  link  is  raised  or  lowered  as  may  be  desired,  by 
means  of  the  system  of  levers  shown.  If  the  link  is  in  the 
position  shown  by  the  dotted  lines  the  engine  will  run  forward, 
that  is,  in  the  direction  of  the  arrow.  The  cut-off  will  occur 
at  the  latest  time  possible  with  this  combination.  The  nearer 
the  block  E  is  to  the  centre  of  the  link,  the  earlier  will  be  the 
cut-cff.  This  system  is  most  extensively  employed  on 
American  locomotives  and  on  some  marine  engines. 


VALVES   AND   VALVE-GEARING. 


223 


224 


STEAM-POWER. 


Another  form  of  link  is  the  Gooch  link.  In  this  contriv- 
ance the  link  remains  stationary  and  the  block  is  moved. 
There  are  many  other  forms  of  valve-gear  for  operating  the 
D-valve,  but  lack  of  space  forbids  their  description  in  this  work. 

The  piston-valve  has  already  been  described  in  Chapter 
XVI.  There  are  a  number  of  modifications  of  the  D-valve 
which  are  used.  They  will  be  described  briefly  below. 

The  Allen  Valve. — This  is  an  ordinary  D-valve  having  a 
steam-passage  around  the  outside  of  the  exhaust-chamber  as 
shown  in  Fig.  179.  This  passage  is  cut  through  the  steam- 
lap  and  so  communicates  with  the  port.  When  the  valve  is 
open  the  maximum  amount,  steam  enters  the  port  from  outside 
as  in  an  ordinary  slide-valve,  and  also  by  means  of  the  passage. 
The  passage  should  be  equal  to  one  half  the  port-opening. 
The  advantage  of  this  valve  is  that  it  works  more  quickly 
than  an  ordinary  D-valve  and  accomplishes  the  same  results 
with  half  the  travel. 


FIG.  180. — Double-ported  Slide-valve. 

The  Double-ported  Valve. — This  valve,  shown  in  Fig.  180, 
accomplishes  the  same  results  as  the  Allen  valve.      One  half 


VALVES  AND   VALVE-GEARING. 


225 


the  steam  enters  the  port  from  the  outside  of  the  valve ;  the 
other  half  enters  through  the  passages  cut  in  the  sides  of  the 
valve  and  leading  to  an  auxiliary  port  in  the  valve-seat,  as 
shown.  The  exhaust  steam  enters  the  exhaust-chamber  in 
two  places,  one  half  coming  over  the  live-steam  passage,  the 
rest  coming  directly  into  the  chamber.  The  area  of  the  steam- 
passage  in  the  valve  at  its  outside  should  be  equal  to  half  the 
area  of  the  auxiliary  port.  It  should  become  smaller  toward 
the  centre  until  it  is  zero  at  the  centre.  The  valve  should  be 
high  enough  to  take  care  of  all  the  exhaust  steam  that  flows 
over  the  steam-passage. 

Gridiron  Valve. — This  consists  of  an  arrangement  of  trans- 
verse openings  and  bars,  covering  a  like  arrangement  in  the 
valve-seat.  There  is  usually  a  valve  for  each  end  of  the 
cylinder.  This  valve  gives  a  wide  opening  with  a  very  short 
travel. 


HIGH    SPEED    AUTOMATIC    CUT-OFF   VALVES. 

The  valves  of  this  class  are  very  numerous.  Only  a  few 
will  be  described. 

The  Meyer  Valve  is  shown  in  Fig.  181.  It  consists  of  a 
plain  D-valve  with  passages  outside  of  the  steam-lap  leading 


FJG.  181.—  The  Meyer  Independent  Cut-off  Valve. 

to  the  top  of  the  valve.  These  passages  are  covered  by  blocks 
which  slide  on  the  valve,  and  which  are  driven  by  a  separate 
eccentric.  Steam  is  allowed  to  enter  the  ports  only  through 


226  STEAM  POWER. 

these  passages.  The  distance  which  separates  the  blocks  can 
be  varied  at  will  by  turning  a  hand-wheel.  This  wheel  turns 
a  right-  and  left-hand  thread  which  causes  the  blocks  to 
approach  or  recede  from  each  other  according  to  the  direction 
of  rotation.  The  blocks  can  be  varied  so  as  to  be  totally 
inoperative  or  to  prevent  steam  from  entering  the  cylinder  at 
any  portion  of  the  stroke. 

TJie  Buckeye  Valve. — This  valve  is  shown  in  Fig.  151. 
The  valve  is  held  to  its  seat  by  balance-pistons  which  are 
extended  by  coiled  springs.  Steam  enters  at  D  and  passes  to 
the  chamber  /  in  the  valve.  Ports  cut  in  these  chambers 
admit  steam  to  the  cylinder.  These  ports  are  covered  by 
sliding-blocks  as  in  the  Meyer  valve.  These  blocks  are  driven 
by  a  separate  eccentric.  The  valve-rod  of  these  blocks  passes 
through  the  main  valve-rod,  which  is  hollow.  The  cut-off  is 
varied  by  the  eccentric  driving  the  blocks,  which  is  rotated  on 
its  shaft  by  the  governor,  for  variations  in  load,  as  will  be 
explained  later. 

The  Ideal  Engine  Valve  has  been  illustrated  in  Fig.  153. 
It  is  of  the  hollow-piston  type.  The  valve  is  driven  by  a 
slotted  eccentric,  which  is  shifted  by  the  governor  on  variation 
of  the  speed.  This  alters  the  travel  of  the  valve,  thus  making 
the  engine  automatic  in  its  action. 

SLOW    SPEED    AUTOMATIC    CUT-OFF   VALVES. 

Corliss  Valves. — A  Corliss  engine  is  operated  by  rotating 
valves  instead  of  slide-valves.  Two  valves  control  the  admis- 
sion and  two  the  exhaust.  These  valves  are  shown  in  section 
in  Fig.  156.  The  two  upper  valves  are  the  admission-valves; 
the  two  lower  are  the  exhaust-valves.  The  valves  are  rotated 

% 

by  links  from  the  wrist-plate  shown  on  the  cylinder  of  the 
engine,  Fig.  155.  The  wrist-plate  is  rotated  by  the  eccentric- 
rod,  through  a  rocker,  as  shown  in  the  figure.  The  rods 
joining  the  valves  to  the  wrist-plate  may  be  altered  in  length 
so  as  to  change  the  admission  cut-off,  release,  and  compression 


AND   VALVE-GEARING. 


227 


FIG.   182. — Armington  and  Sims  Piston-valve. 


FIG.  183.*— Giddings  Valve. 


*  This  valve  takes  steam  internally  as  shown  in  the  figure. 


228 


STEAM-POWER. 


as  may  be  desired.  The  admission-valves  are  opened  by  a 
latch  •  connected  to  the  valve-rods.  This  latch  is  shown  in 
Fig.  184.  A  piece  carrying  two  arms,  CD  and  CA,  rotates 
about  the  centre  C.  C  is  a  point  on  the  axis  of  the  valve. 
Swung  on  a  pivot  at  D  is  a  trip  with  two  arms,  ED  and  FD. 


FIG.  184.— Releasing-gear  of  Corliss  Valve, 

At  E  is  a  notch  which  engages  a  lever  CL,  which  rotates  the 
valve.  The  extremity,  F,  of  the  other  arm  of  the  trip,  when 
the  piece  A  CD  is  rotated,  moves  along  the  circumference  of  a 
circular  piece,  HGK,  which  also  is  centred  at  C.  On  the  cir- 
cumference of  this  piece  is  a  projection,  HG,  which  joins  the 
circumference  by  means  of  a  concave  curve  at  G.  The  valve 
is  connected  to  a  dash-pot  at  J/by  the  rod  LM.  The  piece 
ACD  is  joined  to  the  wrist-plate  by  means  of  the  valve-rod 


VALVES  AND   VALVE-GEARING.  229 

at  A .  The  piece  HGK  carries  an  arm  CL  At  the  point  /  of 
this  arm  a  rod  connecting  with  the  governor  is  attached. 
Now  the  wrist-plate  moves  the  piece  ACD,  causing  the  trip 
EDF  to  rise.  The  notch  at  E  being  engaged  with  the  lever 
LC,  the  valve  is  rotated  and  the  port  opened.  When  the  trip 
has  been  raised  a  certain  distance  the  projection  at  F  on  the 
arm  DF  strikes  the  projection  HG.  The  point  F  is  forced 
away  from  C  and  the  trip  is  rotated  about  D  as  a  centre.  This 
disengages  the  notch  E  from  the  lever  LC,  and  the  released 
valve  is  immediately  closed  by  the  dash-pot  pulling  LG  to  its 
original  position.  As  the  speed  is  varied  the  governor  moves 
the  rod  //,  thus  turning  the  piece  HGK  about  C  and  altering 
the  position  of  HG.  This  will  make  the  cut-off  occur  earlier 
or  later  as  the  case  may  be.  The  exhaust- valves  are  connected 
rigidly  with  the  wrist-plate,  and  having  no  releasing  devices 
are  positively  driven.  The  valve-rods  are  in  two  pieces.  The 
pieces  are  joined  by  a  turnbuckle  with  a  right  and  left  thread, 
so  that  the  rods  may  be  lengthened  or  shortened  at  will. 

A  dash-pot  is  shown  at  M,  Fig.  184.  Its  piston  is  an  air- 
tight fit,  but  a  valve  not  shown  in  the  figure  admits  a  limited 
quantity  of  air  under  the  piston.  The  object  of  the  dash(-=tpot 
is  to  close  the  valve  almost  instantly  as  soon  as  it  is  released 
by  the  trip.  It  also  affords  a  cushion  so  that  the  parts  of  the 
valve-mechanism  are  not  violently  jarred  by  the  sudden 
closing. 

The  governor  of  the  Corliss  engine  is  of  the  fly-ball  typei 
When  the  engine  speeds  up  the  balls  rise,  thus  moving  a  lever 
which  is  attached  to  the  rods  moving  the  piece  GHK  in  Fig. 
184. 

Greene  Engine. — This  engine,  like  the  Corliss,  has  two 
valves  for  admission,  and  two  for  exhaust.  In  the  Greene 
engine,  however,  the  valves  are  flat  slides  instead  of  being 
rotary.  The  operating  mechanism  is  shown  in  Fig.  185.  AB 
is  a  sliding-block,  operated  by  the  eccentric.  It  carries  two 
tappets  C  and  D.  These  tappets  strike  toes  E  and  F  on  the 
rocking  levers  G  and  H  respectively,  which  move  the  valves. 


230 


STEAM-POWER. 


If  the  block  AB  be  moving  in  the  direction  shown  by  the 
arrow,  the  tappet  D  will  engage  the  toe  F,  rotating  it  and  thus 
moving  the  valve.  The  other  tappet  will  pass  under  the  toe 
E\  the  toes  are  beveled  on  the  under  side  and  thus  raise  in 
their  sockets,  when  the  beveled  side  of  the  tappet  come?  in 
contact  with  them.  When  the  tappet  has  passed  the  toe  will 
drop  of  its  own  weight.  The  toe  F  moves  in  the  arc  of  a  circle. 


FIG.  185. — Greene  Engine  Valve-gear. 

Hence  it  will  disengage  the  tappet  after  a  certain  time  and 
drop  into  its  original  position.  On  the  return  stroke  of  the 
block  the  operation  will  be  reversed,  F  rising  in  its  socket  and 
E  rotating.  The  cut-off  is  regulated  by  a  fly-ball  governor 
which  raises  or  lowers  the  plate  K  to  which  the  tappets  are 
attached.  The  lower  the  plate  is,  the  earlier  the  toes  will 
disengage,  thus  making  the  -cut-off  earlier  also. 

HIGH-SPEED    ENGINE-GOVERNORS. 

By  the  use  of  Fig.  1 87  it  may  be  shown  that  by  making  the 
angle  of  advance  less  and  the  travel  greater,  the  cut-off  occurs 
later. 

Also  by  making  the  angle  of  advance  greater  and  the 
travel  less  the  cut-off  occurs  earlier. 

This  principle  is  applied  in  the  construction  of  governors 
for  automatic  cut-off  engines,  an  example  of  which  is  shown 
in  Fig.  1 54. 


VALVES  AMD   VALVE-GEARMG.  231 

The  eccentric  is  not  fast  to  the  shaft  but  swings  about  it 
from  a  pivot  5. 

The  eccentric  proper  is  fastened  to  the  diamond-shaped 
plate  57",  which  is  held  firmly  in  place  by  the  spring  £.  a  is 
the  centre  of  the  shaft  and  //  is  the  centre  of  the  eccentric  disk. 

Hence  ah  =  the  eccentricity. 

When  the  wheel  increases  its  speed,  the  ball  C  moves 
towards  the  rim  of  the  wheel  by  reason  of  centrifugal  force. 

This  causes  H  and  T  to  move  to  the  left  and  with  it  the 
centre  h  of  the  eccentric. 

That  is,  h  moves  towards  a,  thus  making  the  eccentricity 
less  and  making  the  cut-off  occur  earlier,  which  will  tend  to 
cause  the  engine  to  run  slower.  When  the  engine  begins  to 
run  slow  the  ball  C  moves  toward  the  shaft  and  the  cut-off  is 
made  later,  thereby  increasing  the  steam-supply  and  the  speed 
of  the  engine. 

This  is  but  one  of  many  forms  of  high-speed  engine- 
governors.  All  or  nearly  all  operate  by  shifting  the  eccentric. 
Those  having  but  a  single  valve  move  the  eccentric  in  a  slot' 
as  above.  Those  having  multiple  valves,  as  the  Buckeye 
engine,  rotate  the  eccentric  on  the  shaft. 


CHAPTER  XXI. 
VALVE-DIAGRAMS. 

THE  object  of  a  valve  diagram  is  to  show,  graphically,  the 
relations  between  steam  lap,  exhaust  lap,  lead,  travel  of  the 
valve,  port  opening,  the  events  of  the  piston  stroke,  etc.  For 
this  purpose  there  are  several  styles  of  diagrams,  all  of  which 
are  more  or  less  convenient,  but  the  author  prefers  the  Zeuner 
diagram  on  account  of  its  simplicity  and  adaptability. 


FIG.  1 86. 


In  Fig.  186,  let  A  A  i  represent  the  stroke  of  the  piston  and 
the  travel  of  the  valve.  This  may  te  done,  though  the  scale 
will  not  be  the  same  for  both,  as  the  stroke  of  the  piston  is 
always  greater  than  the  travel  of  the  valve.  It  wfll  be  seen 


232 


VALVE  DIAGRAMS.  233 

later,  that  just  what  this  scale  is,  is  of  no  importance.  In  the 
same  figure,  let  O  be  the  center  of  the  crank-shaft  and  a  the 
argle  of  advance. 

When  the  center  of  the  crank  pin  is  at  A ,  the  center  of  the 
eccentric  will  be  at  A'.  Let  the  crank  move  from  its  dead 
center  position  OA  to  any  new  position  OB.  The  eccentric 
will  n:ove  to  the  new  position  OB',  the  angle  AfOBf  being 
equal  to  the  angle  AOB.  Drop  a  perpendicular  from  B  upoi 
A  A  i  and  we  have  Ob  as  the  distance  of  the  valve  to  the  right 
of  mid-position  when  the  crank-pin  has  the  position  B.  The 
principle  of  the  Zeuner  diagram  will  now  be  shown.  Draw 
OA "  making  a',  to  the  left  of  OF  equal  to  a,  the  angle  of 
advance.  From  A"  drop  a  perpendicular  upon  OB,  the  crank 
position  under  consideration.  In  the  triangles  ObB'  and  ObiA", 
the  side  OA"  is  equal  to  the  side  OB',  the  angle  Ob^A"  is 
equal  to  the  angle  ObB'  and  the  angle  BOA"  is  equal  to  the  angle 
AiOB'.  The  two  triangles  are  therefore  equal  in  every  respect 
and  Obi  is  equal  to  Ob.  The  latter  is  the  distance  of  the  valve 
from  mid-position.  Since  OB  is  any  crank  position  it  follows 
that  the  distance  of  the  valve  to  the  right  of  mid-position  for 
any  position  of  the  crank  may  be  found  by  drawing  the  crank 
in  the  desired  position  and  dropping  a  perpendicular  upon  it 
from  A" .  The  distance  from  the  center  of  the  circle  to  this 
intersection  is  the  distance  from  mid-position.  Since  Ob\A"  is 
a  right  triangle  it  follows  that  the  locus  of  the  intersections 
mentioned  above,  of  which  b\  is  one,  will  be  on  a  circle  with 
the  hypothenuse  as  diameter.  We  will  call  this  a  valve-circh. 
Any  crank  position  that  will  intersect  this  circle  will  correspond 
to  a  position  of  the  valve  to  the  right  of  mid-position  and  the 
distance  from  the  center,  O,  to  the  intersection  will  give  the 
cistance  of  the  valve  from  mid-position  for  that  particular 
crank  position.  Prolong  A"O  to  A'"  and  draw  the  circle  with 
OA '"  as  diameter.  Similar  reasoning  will  show  that  crank  posi- 
tions intersecting  this  circle,  correspond  to  positions  of  the  valve 
to  the  left  of  mid-position. 

Consider  now,  the  port  opening. 


234  STEAM-POWER. 

When  the  center  cf  the  eccentric  is  at  F  or  F',  the  valve 
will  have  its  mid-position  and  its  edges  will  lap  over  the  H.E. 
and  C.E.  ports  by  the  amount  of  the  steam  lap  which  may  or 
may  not  be  the  same  on  both  ends.  It  must  therefore  move 
from  this  position  the  amount  of  the  steam  lap  before  the  port 
begins  to  open.  If  the  distance  from  mid-position  is  known, 
the  port  opening  is  found  by  subtracting  the  steam  lap.  The 
same  may  be  said  of  the  exhaust  opening.  This  is  performed 
graphically  by  drawing  the  steam  lap  circle  with  center  O  and 
radius  Oc  equal  to  the  steam  lap,  and  the  exhaust  lap  circle 
with  center  O  and  radius  Od  equal  to  the  exhaust  lap.  The 
distance,  therefore,  measured  along  any  crank  position,  between 
the  lap  circle  and  the  valve  circle  gives  the  port  opening.  For 
example,  the  port  opening  for  the  crank  position  OB  is  eb\. 

Consider  next  the  events  of  the  stroke. 

Admission  and  cut-off  occurs  on  H.E.,  when  the  steam  port 
opening  is  zero  and  the  valve  to  the  right  of  mid-position. 
The  crank  positions  for  these  events  will  therefore  be  those 
passing  through  the  intersections  /  and  g,  positions  on  which  the 
distance  between  the  two  circles  is  zero.  OC  is  therefore  the 
crank  position  for  H.E.  admission  and  OD  crank  position  for 
H.E.  cut-off.  Release  and  compression  occur  when  the  exhaust 
opening  is  zero.  Upon  reflection  it  will  be  seen  also,  that  these 
events  will  occur  on  H.E.,  when  the  valve  is  to  the  left  of  mid- 
position.  The  intersection  of  the  exhaust  lap  circle  with  the 
lower  valve  circle  will  determine  the  crank  position  OE  and  OF 
for  H.E.  release  and  compression,  respectively.  In  a  similar 
manner  OG,  OHj  O/,  and  OJ  are  the  crank  positions  for  ad- 
mission, cut-off,  release,  and  compression,  respectively  on  the 
crank  end.  For  the  dead  center  crank  position  OA,  the  port 
opening  is  ch,  which  is  therefore  head-end  lead.  The  maximum 
H.E.  port  opening  is  }A"  when  the  crank  has  the  position  OA". 

Fig.  187  is  a  complete  Zeuner  diagram.  By  its  use,  practi- 
cally all  problems  concerning  the  simple  valve  gears  may  be 
solved.  A  study  of  some  of  its  geometric  properties  will  be 
profitable. 


VALVE-DIAGRAMS. 


235 


(1)  The  line   A" A'"   divides    the    diagram    symmetrically. 
Proof:    Of  =  Og,  therefore  the  angle  CO4"-the  angle  DO  A" 
and  OA"  bisects  DOC.    Likewise  OA"f  bisects  GOH . 

(2)  The  line  gA"  is  tangent  to  the  steam  lap  circle  and 
perpendicular  to  OD  at  g,  because  the  triangle  OgA"  is  inscribed 
in  a  semicircle. 

(3)  The  line  CD  is  perpendicular  to  A"O  and  tangent  to  the 
steam  lap  circle.     Proof:    The  line  OA"  bisects   the  triangle 
DOC,  which  is  isosceles,  and  is  therefore  perpendicular  to  CD. 


FIG.  187. 

Oj  =  Og  because  the  triangle  OgA"  =  the  triangle  OjD.     CD  is 
therefore  tangent  to  the  steam  lap  circle. 

Similar  reasoning  will  show  that  GH,  EF  and  JI  are  also 
tangent  to  their  respective  lap  circles  and  perpendicular  to 
A"  A'". 

(4)  The  line  A"h  is  perpendicular  to  AO  because  the  angle 
Oh  A",  being  inscribed  in  a  semicircle,  is  a  right  angle. 

(5)  The  circle  with  radius  AM  and  center  A,  and  tangent  to 
CD,  equals  the  lead  ch. 


236 


STEAM-POWER. 


Proof:  Draw  AK  parallel  to  CD.  The  triangles  AOK  and 
A"hO  being  right  triangles  with  equal  hypotheunse  and  a  com- 
mon angle  are  equal  in  every  respect,  hence  OK=Oh  and 


As  an  example  of  the  application  of  the  foregoing  principles 
in  the  solution  of  a  typical  problem,  let  us  consider  an  engine 
in  which  the  valve  travel  is  4-inches,  H.E.  steam  lap  f-inch, 
C.E.  steam  lap  H-inch,  H.E.  exhaust  lap  f-inch,  C.E.  exhaust 


Valve  to  right 


C.O.H.E. 

Comp.  C.E. 


Rel.  H.E. 
Adm.  C.E. 


Valve  to  left 


FIG.  1 88. 

lap  &-inch,  angle  of  advance  40°,  and  the  ratio  of  the  length  of 

7? 
the    crank  to  the  length  of  the  connecting-rod  =  y  =  — .     This 

**     5 
data  is  for  a  valve  which  takes  steam  on  the  outside,  as  for  a 

plain  D  valve  and  the  engine  is  to  "run  over."  It  is  required 
to  determine  the  positions  of  the  crank  for  all  events  and  the 
per  cent  of  stroke  at  which  they  occur. 

With  radius  OA  =2*  inches  and  center  O,  Fig.  188,  draw  the 

*  Fig.  1 88  is  drawn  to  a  reduced  scnlc. 


VALVE-DIAGRAMS.  237 

crank  and  eccentric  circle.  Lay  off  the  angle  of  advance  =  40°, 
as  shown,  OA  will  be  the  H.E.  dead  center  and  OA\,  the  C.E. 
dead  center.  Lay  off  the  two  valve  circles  on  the  line  A"A'n. 
With  radius  Oa  =  |-inch  and  radius  O6  =  ii-inch,  draw  the  H.E. 
and  C.E.  steam  lap  arcs.  With  radius  Oe  =  f-inch  and  radius 
Od  =  &-'mchj  draw  the  H.E.  and  C.E.  exhaust  lap  arcs. 

Through  the  center  O  and  the  intersections  of  the  lap  arcs 
with  the  valve  circles,  draw  the  eight  lines  representing  the 
positions  of  the  crank  for  each  of  the  events  H.E.  and  C  E. 
A  consideration  of  the  principles  laid  down  on  page  234  with 
reference  to  whether  the  valve  is  to  the  right  or  left  of  mid-posi- 
tion, also  the  "right  and  left"  valve  circles,  will  serve  as  a  guide 
for  naming  the  event  corresponding  to  each  of  these  crank  posi- 
tions. These  are  marked  for  the  present  problem. 

In  order  to  determine  the  per  cent  of  stroke  at  which  these 
events  occur  it  is  necessary  to  take  into  account,  the  effect  due 
to  the  angularity  of  the  connecting-rod.  On  account  of  the 
large  ratio  between  the  length  of  the  eccentric-rod  and  the 
eccentricity,  it  is  usual  to  neglect  the  angularity  of  the  eccentric- 
rod.  It  was  for  this  reason  that  the  data  7-  =  —  was  given.  It 

*•     5 

will  be  remembered  that  AA\  represents  the  stroke  as  well  as 
the  valve  travel,  and  OA  therefore  represents  the  length  of  the 
crank  R.  The  length  of  the  connecting-rod  will  therefore  be 
$R.  Let  us  determine  the  per  cent  of  stroke  of  the  piston  at 
which  H.E.C.O.  occurs.  With  a  radius  =  5^  strike  the  arc  MN. 

-  =  — =77i%.     The  others  may  be  found  in  the  same 
AA\  4 

way,  the  head  end  events  being  measured  from  A  and  the  crank 
end  events  from  A  \. 

An  engine  is  said  to  "run  over"  when  a  point  on  its  fly- 
wheel rises  past  that  part  of  the  engine  between  the  crank-shaft 
and  the  cylinder.  When  it  runs  in  the  other  direction  it  is  said 
to  "run  under." 

A  "  direct  valve  "  is  one  which  takes  steam  from  the  outside, 
as  in  the  ordinary  plain  D  slide  valve.  An  "  indirect  valve  "  is 


238 


STEAM-POWER. 


one  which  takes  steam  from  the  inside  as  in  the  piston  valve,  see 
Fig.  182.  It  is  evident  that  with  the  direct  valve,  cut-off  and 
admission  occur  on  H.E.  with  the  valve  to  the  right  of  mid- 
position  and  release  and  compression  on  H.E.  with  the  valve  to 
the  left  of  mid-position.  For  an  indirect  valve,  admission  and 
cut-off  occur  with  the  valve  to  the  left,  and  release  and  compres- 
sion with  the  valve  to  the  right  of  mid-position  on  H.E.  The 
diagrams,  so  far,  have  been  for  an  engine  running  over  with  a 


DIRECT  VALVE 


FIG.  189. 

Valve  to  left 


Valve  to  left 
Valve  to  left     INDIRECT  VALVE 


Valve  to  .right 
FlG.  190. 


,  Valve  to  left 
FIG.  igoa. 


direct  valve.  It  has  been  assumed  also  that  the  piston  and 
valve  were  to  the  left  of  the  crank  shaft,  as  is  1  igs.  138  and  139, 
making  A,  in  Figs.  186  and  187,  the  H.E.  dead-center.  This 
will  be  assumed  for  all. 

Figs.  1 88,  189,  190,  and  1900  show  the  forms  of  Zeuner  dia- 
grams for  the  conditions  marked.  In  each  figure,  A  is  H.E. 
dead-center  and  A'  the  corresponding  position  of  the  eccentric 


VALVE-DIAGRAMS  239 

center,  a,  as  before,  is  the  angle  of  advance.  It  will  be  seen 
that  with  an  indirect  valve,  the  eccentric  follows  the  crank, 
instead  of  preceding  it,  as  with  the  direct  valve.  Angle  of 
advance  for  an  indirect  valve  may  therefore  be  defined  as  90°, 
minns  the  angle  by  which  the  crank  precedes  the  eccentric. 

PROBLEMS. 

1.  An  engine  with  a  direct  valve  and  running  over,  has  a  valve 
travel  of  3^",  steam  lap  H.E.  and  C.E.  J",  exhaust  lap  H.E.  and 

C.E.  J">  lead  j"  and  7-=—.     Construct  a  Zeuner  diagram  and  find 

**      5 
the  crank  position  for  all  events,  H.E.  and  C.E. 

2.  Using  the  Zeuner  as  constructed  in  the  above  problem,  deter- 
mine the  per  cent  of  stroke  at  which  each  of  the  events  occurred. 

3.  An  engine  with  a  direct  valve  and  running  under,  furnishes  the 
following    data:     Valve   travel   4",  steam  lap   H.E.    f",    steam    lap 
C.E.  f",  exhaust  lap  H.E.  f",  exhaust  lap  C.E.  f",  angle  of  advance 

30°,  and  Y  =  —.     Construct  a  Zeuner  diagram  and  find  crank  posi- 

*•      5 
tions  for  all  events. 

4.  An  engine  with  a  direct  valve  and  running  over,  has  the  fol- 
lowing data*    Valve  travel  4",   lead   &",  cut-off  H.E.    75%,   release 

H.E.  94%,  and  j-  —  -~ •  The  valve  is  to  have  equal  steam  and  ex- 
haust laps  for  the  two  ends.  Construct  a  Zeuner  diagram  and  deter- 
mine steam  and  exhaust  laps,  and  locate  crank  positions  for  all  events. 

5.  Engine  with  direct  valve  and   running  over,  steam   lap   H.E. 
and  C.E.  }",  C.O.  H.E.   60%,  compression  C.E.  15%,  lead  j"  and 

7   =— .     Construct  Zeuner  diagram  and  determine  angle  of  advance, 

valve  travel  and  exhaust  lap.  Locate  crank  positions  for  all  events 
H.E.  and  C.E. 

NOTE. — Determine  first,  the  point  c  as  shown  in  Fig.  186,  then  the 
point  h.  Next  determine  the  crank  position  for  cut-off  H.E.,  the  per 
cent  of  which  is  given.  To  do  this  draw  any  crank-pin  circle,  and 
on  its  horizontal  diameter  locate  a  point  60%  from  H.E.  dead  center. 
With  a  radius  equal  to  5  times  the  assumed  radius  of  crank  circle 


240  STEAM-POWER. 

draw  an  arc.  Through  center  of  circle  and  the  intersection  of  this 
arc  and  circle  draw  a  line.  It  will  be  the  true  position  of  the  crank 
for  cut-off  H.E.  Proceed  according  to  propositions  3  and  4,  page  235. 

6.  The  engine  of  problem  i  is  to  be  set  to  give  a  lead  of    J"  on 
each  end.     Find  the  angle  of  advance  in  degrees. 

7.  A  D-valve  used  on  an  engine  running  over,  the  sum  of  whose 
steam  laps  is  ij''  and  the  sum  of  whose  exhaust  laps  is  J",  is  to  be 
set  to  give  cut-off  at  75%  on  both  ends.     The  valve  travel  is  3"  and 

?L=- 

L~  S 

Find  the  angle  of  advance,  steam  lap,  exhaust  lap,  and  maximum 

port  opening  (H.E.  and  C.E.). 

NOTE. — The  steam  and  exhaust  laps  will  not  be  the  same  on  both 
ends,  but  as  their  sums  are  known,  the  lines  CD  and  GH,  Fig.  187, 
may  be  determined.  Using  the  given  data,  locate  D  and  H.  With  radius 
equal  to  the  sum  of  the  steam  laps  and  center  D,  draw  an  arc  to 
which  HG  will  be  tangent  when  drawn.  With  same  radius  and  cen- 
ter H,  draw  another  arc  to  which  CD  will  be  tangent  when  drawn. 
CD  and  HG  may  then  be  drawn  tangent  to  these  arcs.  The  differ- 
ence between  the  H.E.  and  C.E.  exhaust  laps  will,  of  course,  be  the 
same  as  that  between  the  H.E.  and  C.E.  steam  laps. 

8.  Engine  running  over  with  indirect  valve.     Valve  travel  3",  lead 

$",  angle  of  advance  40°,  exhaust  lap  f",  and  7-  =  —. 

*•      5 
Construct  a  Zeuner  diagram  and  find  crank  position  for  all  events 


CHAPTER   XXII. 
ROTARY   ENGINES   AND    STEAM-TURBINES. 

To  this  type  of  engine  belong  all  those  engines  having  a 
rotary  piston  instead  of  the  reciprocating  piston,  as  in  the 
ordinary  engine. 

The  steam  enters  the  cylinder  directly  from  the  boiler 
without  passing  through  the  intermediate  steam-chest. 

The  area  of  the  piston  against  which  the  steam  presses  is 
really  an  enlargement  of  the  crank-pin.  The  piston  must 
make  a  steam-tight  fit  with  the  circumference  and  the  ends  of 
the  cylinder,  and  the  steam  must  be  controlled  so  as  to  exert 
its  pressure  on  the  surface  of  the  piston  and  then  be  allowed 
to  escape.  There  must  therefore  be  the  pressure  of  the  steam 
on  one  side  and  the  pressure  of  the  atmosphere  on  the  other 
side.  The  arrangement  used  to  take  the  place  of  the  valve  in 
the  ordinary  engine  for  separating  the  steam  and  exhaust 
openings  is  usually  called  the  abutment. 

Every  rotary  engine  must  have  an  abutment  and  a  piston. 

Rotary  engines  may  be  divided  into  two  classes, — those 
in  which  the  abutment  and  piston  interchange  their  functions 
and  those  in  which  the  abutment  remains  abutment  and  the 
piston  remains  piston. 

Fig.   191  is  an  example  of  the  former  class. 

The  steam  from  the  boiler  enters  at  A  and .  the  exhaust 
steam  passes  out  through  B. 

In  the  position  shown  in  the  figure,  D  is  acting  as  the 
piston  and  C  is  the  abutment.  The  pressure  on  the  two  long 

241 


242 


STEAM-POWER. 


ends  of  C  having  equal  leverage  on  each  end,  there  is  no  turn- 
ing effect  produced  by  C,  hence  it  acts  only  to  control  the 
steam.  However,  the  steam-pressure  coming  against  the 
lower  end  of  D  rotates  it  in  a  direction  opposite  to  the  hands 

THE    ENGINE. 


FIG.  191.  — Rotary  Engine. 

of  a  watch  until  it  reaches  a  position  similar  to  that  held  by  C, 
when  it  becomes  abutment  and  C  becomes  piston.  It  is  seen 
that  the  two  wheels  have  projections  in  their  perimeters  gearing 
with  each  other.  The  engine  has  only  one  shaft,  but  by  this 
gearing  together  the  effort  of  both  wheels  is  utilized.  In  this 


ROTARY  ENGINES  AND  STEAM-TURBINES.  243 

design  the  steam-joint  between  the  piston  and  cylindrical  part 
of  the  casing  is  made  by  the  use  of  packing  which  is  pressed 
out  radially  by  the  means  of  springs.  The  steam-joint  between 
the  piston  and  the  flat  sides  of  the  casing  is  made  by  the  use 
of  radial  packing-strips  as  shown  in  the  figure. 

In  this  design  it  is  evident  that  there  is  no  expansion  of 
steam  except  from  the  boiler.  It  is  also  noticeable  that  there 
is  to  the  right  of  D  a  large  clearance-space,  containing  steam 
which  exerts  no  effort  whatever. 

Fig.  192  illustrates  the  type  of  rotary  engine  in  which  the 
abutment  and  piston  do  not  change  their  functions.  C  is  the 


FIG.  192. 

abutment  and  D  is  the  piston.  Steam  here  acts  to  produce 
motion  in  a  direction  contrary  to  the  hands  of  a  watch  because 
there  is  less  pressure  to  the  right  of  the  lower  part  than  to  the 
left. 

The  advantages  of  the  rotary  engine  may  be  summed  up 
as  follows: 


244  STEAM-POWER. 

There  are  no  reciprocating  parts,  and  for  that  reason  no 
resistance  caused  by  the  inertia  of  heavy  mechanism.  There 
is  no  dead-point,  which  is  evident  from  either  one  of  the  figures 
shown. 

Their  construction  being  simple  and  without  the  necessity 
of  converting  reciprocating  motion  into  rotary  motion,  it  occu- 
pies small  space. 

There  being  no  valve-gearing,  the  friction  is  small  and  the 
cost  is  light. 

It  requires  very  little  skill  to  operate. 

The  disadvantages  are  as  follows : 

The  revolving  piston  is  hard  to  pack  so  that  it  will  not 
leak,  as  the  pressure  changes  for  different  parts  of  the  revolu- 
tion, causing  a  strain  which  soon  wears  away  the  packing. 

As  has  been  stated  before,  there  is  necessarily  a  large  clear- 
ance-space requiring  steam  which  exerts  no  rotative  action. 
There  is  no  expansion  of  steam.  It  is  evident  then  for  the 
last  two  reasons  the  rotary  engine  is  very  uneconomical  in  the 
use  of  steam. 

The  expansive  action  of  steam  which  cannot  be  obtained 
with  the  single  rotary  engine  is  sometimes  effected  by  placing 
two  or  more  of  them  on  the  same  shaft,  the  steam  from  the  first 
one  being  exhausted  into  the  next  one  of  a  larger  diameter, 
and  so  on. 

By  this  means  economy  may  be  practised  to  some  degree. 

Owing  to  the  large  waste  of  steam  these  engines  are  not 
used  to  a  large  extent.  Rotary  engines  formerly  had  their 
largest  application  on  steam  fire-engines,  driving  rotary  pumps; 
but  even  for  this  purpose  they  have  been  largely  displaced  by 
reciprocating  engines,  driving  reciprocating  pumps. 

STEAM-TURBINES. 

The  steam-turbine  is  similar  to  the  rotary  engine  in  that  it 

produces  a  direct  rotary  motion  without  any  reciprocating  parts. 

It  consists  of  a  small  turbine-wheel  which  runs  by  steam 


ROTARY  ENGINES  AND  STEAM-TURBINES. 


245 


as  the  ordinary  turbine  does  by  water.  It  is  interesting  to 
note  the  fact  that  the  first  engine  of 
which  history  gives  us  any  knowledge 
was  Hero's  engine  known  as  a  "reac- 
tion-wheel "  about  120  B.C.  In  1629 
Branca  proposed  one  similar  to  it,  the 
form  of  which  is  substantially  appro- 
priated in  some  of  the  modern  makes  of 
turbines.  These  two  turbines  (Hero's 
and  Branca 's)  furnished  the  principal 
features  of  the  two  types  of  modern 
steam-turbines. 

The  rotary  speed  of  the  modern  steam-turbine  exceeds  greatly 
that  of  the  ordinary  reciprocating  end  -e.     The  efficiency  of  the 


FIG.  193. — Hero's  Engine. 


FIG.  194. — Branca's  Engine. 

steam-turbine  is  computed  by  Prof.  Thurston  to  be  about  87 
per  cent,  without  allowing  for  waste.  The  steam-turbine  has 
the  advantage  of  requiring  very  small  floor-space  as  compared 
with  the  reciprocating  engine;  radiation  of  heat  from  the 
heated  surfaces  of  the  engine  is  small  and  the  condensation 
losses  caused  by  the  constant  changing  of  temperature  in 
cylinders  is  here  avoided.  It  is  comparatively  simple  in  prin- 


246 


STEAM-POWER. 


ciple  and  inexpensive  in  construction  and  by  good  designing 
may  be  made  to  attain  great  economy  in  the  use  of  steam. 

Fig-  J93  represents  Hero's  engine,  probably  the  first 
engine  ever  made.  Its  essential  feature  is  a  steam  reaction- 
wheel.  Steam  is  admitted  into  the  sphere  through  the  hollow 
axles  or  trunnions.  As  the  steam  escapes  into  the  atmos- 
phere the  sphere  revolves  in  a  direction  opposite  to  that  of  the 
flow  of  the  steam  from  the  nozzles,  which  motion  is  due  to  the 
reaction  of  the  atmosphere. 

Fig.  194  represents  Branca 's  steam-engine,  A.D.  1629. 
It  consists  of  a  wheel  containing  vanes  upon  its  circumference, 
against  which  a  jet  of  steam  acts  directly. 

The  principles  contained  in  one  or  the  other  of  these  two 
constructions,  principally  the  latter,  have  been  used  in  the 
modern  steam-turbines. 

The  principle  of  the  De  Laval  steam  turbine  is  shown  in 
Fig.  196.  Fig.  195  is  a  sectional  plan.  The  steam  enters  the 


FIG.  195. 

wheel  case  through  several  nozzles,  depending  upon  the  size  of 
the  turbine,  and  leaves  at  the  opposite  side  of  the  wheel.  It 
will  be  seen  that  the  nozzles  diverge  towards  the  turbine.  By 


ROTARY  ENGINES  AND  STEAM-TURBINES.  247 

this  means,  the  expansive  property  of  the  steam  is  utilized  in 
producing  a  high  velocity.  The  high  velocity  of  the  steam 
causes  a  correspondingly  high  velocity  of  rotation  of  the  turbine 


FIG.  196. — De  Laval  Turbine. 

wheel,  the  R.P.M.  varying  from  10,000  to  30,000.  Referring  to 
Fig.  195,  the  steam  enters  the  steam  chest  D  through  the  steam 
pipe  in  which  is  situated  a  throttling  governor.  From  D,  the 
steam  passes  through  the  nozzles  to  the  turbine  wheel  A  which 
revolves  in  the  wheel  case  F.  From  the  wheel  it  passes  to  the 
exhaust  chamber  G,  and  from  there  to  the  atmosphere  or  to  a 
condenser.  The  very  high  speed  makes  it  impossible  to  use 
fixed  bearings,  the  shaft  being  made  very  srrall  and  flexible,  so 
that  it  will  revolve  about  its  center  of  mass,  instead  of  its  geo- 
metric axis.  The  bearings  T  and  S  are  made  movable  so  that 
they  may  adjust  themselves  to  the  movement  of  the  shaft. 
They  are  so  constructed  as  to  prevent  the  escape  of  steam.  The 
speed  of  this  shaft  is  too  high  to  be  used  direct  for  power  pur- 
poses. Helical  gears  are  used  to  reduce  it  in  a  ratio  of  10  to  i, 
L  being  the  power  shaft.  The  slant  of  the  teeth  is  opposite,  on 
the  two  pairs,  in  order  to  avoid  end  thrust  on  the  shaft. 

The  principal  difficulty  with  this  machine  is  its  high  speed, 
which  necessitates  the  use  of  expensive  reducing  gears  and  causes 


248 


STEAMPOWER. 


trouble  with  the  bearings.     This  is  avoided  in  the  Parsons  Tur- 
bine by  expanding  the  steam  against  the  buckets  of  the  turLine 
wheel  itself,  doing  away  with  the  high  velocity  of  steam,  due 
to  expanding  it  in  diverging  nozzles  before  reaching  the  wheel, 
fig.  197  is  an  elevation  showing  the  principle  of  the  Parsons 


Stationary  Bl  des 


uuquo 

])  J)  1)  M)  FTJJ 


Mo 


cuccmc 


Stationary  Blades 


ing  Blades 


)) 


Moving  Blades 


FIG.  197. 

turbine.  Steam  at  boiler  pressure  and  comparatively  small 
velocity  strikes  the  fixed  blade  at  P,  is  reflected  to  the  moving 
blade  at  PI,  causing  the  latter  to  revolve.  The  steam  is  again 
reflected  at  PI,  to  another  moving  blade,  and  so  on.  This 
is  evidently  a  combination  of  the  impulse  and  reaction  types 
shown  in  the  Branca  and  Hero  machines. 

Fig.  198  shows  this  turbine  in  detail.  Steam  enters  at  S, 
passes  through  the  throttling  governor  V,  through  the  port 
A  to  the  rotor  at  the  right  hand  and  small  end.  Here  it  strikes, 
alternately,  the  fixed  and  moving  vanes  which,  it  will  be  noticed, 
increases  in  size  from  right  to  left.  By  this  means,  as  well  as 
by  the  two  enlargements  of  the  rotor  diameter,  opportunity  for 
expansion  of  the  steam  is  allowed.  After  traveling  through  the 
entire  set  of  bucket  wheels,  the  steam  passes  into  the  exhaust 
chamber  B,  and  then  to  the  atmosphere  or  a  condenser.  The 
passage  of  the  steam  through  the  turbine  from  end  to  end, 
tends  to  produce  a  thrust  toward  the  left.  This  is  counter- 
acted by  the  three  balance  pistons  P,  which,  by  means  of  pipes 
E,  are  connected  with  equal  diameters  of  the  rotor.  This 


ROTARY  ENGINES  AND  STEAM-TURBINES. 


249 


turbine  runs  at  a  comparatively  low  speed,  1200  to  3600  R.P.M., 
yet  this  is  too  high  for  fixed  bearings.  Arrangement  is  made 
for  allowing  the  rotor  to  revolve  about  its  center  of  mass,  as  in 
the  De  Laval.  In  this  machine,  however,  the  shaft  is  not 
flexible,  the  bearings  being  made  to  take  care  of  the  entiie 
movement.  These  bearings  consist  of  concentric  rings,  sub- 
merged in  oil,  and  the  play  between  the  rings  suffices  for  the 
movement  necessary.  The  oil  prevents  leakage  of  steam  past 
the  bearings.  The  centrifugal  governor  is  shown  at  the  upper 
right  hand.  It  is  operated  by  a  worm  gear  from  the  shaft. 
At  V8  is  another  valve  operated  by  the  governor.  It  opens 


FIG.  198. 

only  when  the  load  becomes  greater  than  normal,  and  ad- 
mits steam  into  the  middle  set  of  bucket  wheels.  This,  of 
course,  is  done  at  the  expense  of  complete  expansion  and 
economy.  At  the  right  will  be  seen  a  thrust  bearing  which 
is  for  the  purpose  of  keeping  the  rotor  in  its  proper  place,  and 
to  preserve  the  proper  clearance  between  moving  and  fixed 
blades.  Though  this  machine  has  the  advantage  of  low  speed, 
it  requires  better  machine  work  as  the  clearance  between  fixed 


250 


STEAM-POWER. 


and  moving  vanes  has  to  be  very  small,  owing  to  the  fact  that 
expansion  takes  place  within  the  vanes.  It  also  requires  an 
excessively  large  number  of  bucket  wheels.  The  impact  action 
of  the  steam  upon  the  vanes  in  the  De  Laval  turbine  makes  large 
clearances  and  less  machine  work  possible. 


Steam  Chest 


Nozzfe 


Moving  Blades 
Stationary  Blades 
Moving  Blades 


Xozzle  Diaphragm 


»    Moving  Blades  /- 
Stationary  Blades 

Moving  Blades  )  )"H 


I    !     I      !      I      I 

FIG.   1980 — Diagram  of  Nozzles  and  Buckets  in  Curtis  Steam  Turbine. 

The  Curtis  turbine  shown  in  principle,  in  Fig.  1980,  is  really 
a  combination  of  the  p.inciples  of  the  De  Laval  and  the  Par- 
sons turbines.  The  steam  enters  at  the  top  and  is  partially 
expanded  in  diverging  nozzles,  converting  part  of  the  energy  into 
velocity.  This  part  of  the  process  is  similar  to  the  De  Laval. 
The  steam,  with  increased  velocity,  now  enters  the  bucket  wheels, 
similar  to  those  of  the  Parsons  and  is  again  expanded,  doing  work. 


ROTARY  ENGINES  AND  STEAM-TURBINES. 


251 


In  the  noncondensing  turbine  the  steam  is  expanded  directly 
into  the  atmosphere  from  the  upper  set  of  vanes.  In  the  con- 
densing turbine,  however,  it  passes  through  another  set  of 


FIG.  1986. 


diverging  nozzles  and  vanes.  These  two  sets  are  in  entirely 
separate  chambers,  and  are  known  as  "  high  pressure"  and 
"  low  pressure  "  respectively.  By  thus  giving  the  steam  a  higher 


252 


STEAM-POWER. 


initial  velocity,  the  number  of  bucket  wheels  required  is  de- 
creased. The  R.P.M.  is  decreased  by  making  the  wheels  of 
relatively  large  diameter.  The  valves,  shown  at  the  top,  are 
operated  by  the  governor,  the  number  of  open  ones  depending 
upon  the  load.  By  this  means  there  is  full  pressure  in  the 
steam  chest  at  all  times,  the  loss  of  energy,  due  to  expansion 
past  the  usual  governor  valve,  without  doing  work,  being  avoided. 
This  machine  differs  from  the  others  in  being  vertical.  Its 
appication  has  been  principally  in  electric  dynamo  driving,  the 
dynamo  being  direct  connected  and  above  the  turbine.  The 


FIG. 

entire  weight  is  supported  by  a  single  step  bearing,  upon  which 
the  end  of  the  shaft  rests.  The  great  pressure  upon  so  small  an 
area  would  cause  heating,  but  for  the  fact  that  oil  is  forced  in 
under  pressure  great  enough  to  separate  the  surfaces  of  the 
shaft  and  bearing.  Fig.  1986  shows  a  vertical  view  of  this 
machine. 

Fig.  igSc  is  an  illustration  of  another  principle  in  turbine 
construction.  It  is  the  Kerr  steam  turbine.  The  rotor  consists 
of  a  shaft  with  a  number  of  bucket  wheels,  each  wheel  revolving 
in  a  separate  chamber.  The  steam  enters  a  chamber  at  one 


ROTARY  ENGINES  AND  STEAM-TURBINES.  253 

through  a  number  of  nozzles,  so  situated  as  to  direct  jets  of 
btea  m  against  the  buckets  which  are  of  the  same  form  as  those 
u;  ed  on  the  Pelton  water  motor,  Fig.  254.  The  number  of  these 
nozzles  for  each  wheel  depends  upon  the  size  of  the  machine. 
After  the  steam  acts  upon  the  first  wheel  it  expands  through  a 
set  of  nozzles  similar  to  those  already  described,  into  the  next 
chamber,  where  it  acts  upon  the  second  bucket  wheel. 

In  like  manner  it  passes  successively  through  all  the  cham- 
bers, arriving  at  the  last  one  with  a  low  pressure,  from  whence 
it  is  exhausted  to  the  atmosphere,  or  into  a  condenser.  The 
nozzles  direct  the  steam  against  the  buckets  in  their  own  plane. 
There  is,  therefore,  no  end  thrust  upon  the  shaft.  As  each 
wheel  revolves  in  a  medium  of  constant  pressure,  there  is  no 
need  of  small  clearance  between  the  stationary  and  moving 
parts,  hence  the  amount  of  machine  work  is  reduced.  By  divid- 
ing the  expansion  into  several  stages,  the  velocity  of  rotation  is 
made  relatively  small.  The  speed  is  regulated  by  a  throttling 
centrifugal  governor  in  the  steam  pipe. 

One  of  the  principle  sources  of  heat  loss  in  reciprocating 
steam  engines  is  that  of  initial  condensation  and  re-evapora- 
tion, due  to  the  reversal  of  conditions  at  each  stroke.  The 
steam  turbine  avoids  this.  The  reciprocating  engine  also  causes 
vibrations,  which  require  large  foundations  for  their  absorption. 
This,  also,  is  not  the  case  with  the  continuously  revolving  tur- 
bine. On  the  other  hand  the  high  speed  of  the  turbine  requires 
the  best  of  metal  and  workmanship  for  the  rotating  parts. 


APPENDIX   TO   PART   II. 


APPENDAGES  TO   ENGINES. 

THE  articles  described  in  this  chapter  are  used  with  engines 
in  order  to  effect  their  best  working.  They  may  or  may  not 
be  used;  in  fact,  it  will  be  found  that  many  engines  are  run 
without  some  of  them,  at  least. 

Lubricator. — Owing  to  the  pressure  of  the  steam  within  an 
engine-cylinder,  an  ordinary  oiler  as  applied  to  common  bear- 
ings cannot  be  used  to  lubricate  the  piston-  and  slide-valve 
for  the  reason  that  the  steam-pressure  will  not  allow  the  oil  to 
enter.  For  this  purpose  lubricators  are  used  which  force  the 


FIG.  199. — The  "Detroit"  Lubricator. 

oil  in  by  steam-pressure.      They  are  usually  connected  to  the 
steam-pipe  just  above  the  point  where  it   enters   the   steam- 

2S4 


APPENDIX   TO  PART  11. 


255 


chest.     The  illustration  shows  a  sight-feed  lubricator  in  section, 
and  the  manner  of  connecting  it. 

B  is  the  steam-pipe  just  above  the  steam-chest.  A  is  a 
chamber  containing  cylinder-oil.  F  is  a  pipe  connecting  the 
top  of  the  lubricator  to  the  steam-pipe  above,  usually  about 
3  feet  long.  K  is  another  connection  with  the  steam-pipe. 
J  is  a  glass  tube  which  shows  the  level  of  oil  in  A . 

The  operation  of  the  apparatus  is  as  follows:  The  chamber' 
/'provides  for  the  condensation  of  steam  which  enters  through 
the  pipe  F.  This  water  of  condensation  passes  down  through 
the  valve  D  and  through  the  tube  P  and  discharges  into  the 
bottom  of  the  oil-chamber  A .  This  chamber  is  filled  with  oil 
before  starting.  A  drop  of  condensed  water  enters  the  bottom 
of  A  and  displaces  an  equal  bulk  of  oil,  because  of  its  greater 
specific  gravity,  and  this'  drop  of  oil  is  forced  out  through  S, 
past  the  regulating-valve  Ey  making  its  appearance  in  the 
feed-glass  //,  through  K,  and  then  to  the  cylinder  and  valve. 

Separator. — A  considerable  quantity  of  steam  is  condensed 
in  the  steam-pipe  between  a  boiler  and  its  engine. 

Water  is  also  carried  over  in  the 
steam,  due  to  the  disturbances  on  the 
surface  of  the  water  in  the  boiler. 

As  water  is  incompressible,  it  is 
dangerous  to  an  engine  to  pass  water 
through  the  cylinder. 

In  order  to  catch  this  water  which 
is  in  the  steam  and  prevent  it  from 
entering  the  engine,  a  separator  is 
attached  to  the  steam-pipe  near  the 
engine. 

The  accompanying  illustration 
shows,  in  section,  a  separator  which  is 
very  simple  in  principle  as  well  as 
construction.  It.  is  attached  to  the  FlG  200 

steam-pipe    near    the    engine,    so   that  Steam-separator, 

the  steam-passage  is  as  indicated  by  the  arrows. 


256 


STEAM-POWER. 


The  water  in  the  steam  drops  to  the  bottom,  while  the 
steam  passes  on  and  out.  The  water  is  drained  off  from  the 
bottom. 

Oil-separators.  —  Steam-plants  which  use  condensed 
exhaust  steam  for  feed-water  require  some  arrangement  for 


m  m  m_ 


TET 


TTT 


FIG.  201. — Oil-separator. 

separating  oil  and  water  from  the  exhaust  steam  which  has 
cylinder-oil  in  it.  Oil  is  very  prejudicial  to  steam-production, 
as  it  will  combine  with  any  dirt  or  mud  in  the  boiler-water,  to 
form  a  scale,  which  settles  on  the  tubes  and  retards  the  passage 
of  heat  to  the  water.  If  this  oil-scale  becomes  too  thick  it 
may  cause  the  tubes  or  shell  of  the  boiler  to  burn  out. 
An  illustration  of  an  oil-separator  is  here  given. 


PART  III. 

PUMPS,   GAS-ENGINES,   WATER-POWER, 
COMPRESSED  AIR,   ETC. 


CHAPTER    XXIII. 
PUMPING-MACHINERY. 

FORMERLY  pumps  were  used  only  to  raise  water.  At  the 
present  time,  however,  pumps  are  used  for  many  other  pur- 
poses; such  as  feeding  water  against  steam-pressure  into  a 
boiler,  furnishing  water-pressure  for  hydraulic  machines  such 
as  a  hydraulic  press,  for  irrigating,  for  forcing  water  or  other 
fluids  through  long  lines  of  piping  for  water- works  supply,  and 
others  too  numerous  to  mention. 

A  pump  usually  consists  of  a  reciprocating  plunger  or 
piston  working  within  a  cylinder,  but  it  may  be  a  revolving 
wheel  with  buckets  upon  its  periphery  or  something  resembling 
buckets  such  as  vanes  producing  an  inductive  action. 

The  reciprocating  pump  is  of  two  kinds:  The  suction  or 
atmospheric  pump,  and  the  force-pump.  The  principle  of 
action  of  these  two  classes  of  pumps  is  shown  by  diagrams  in 
Figs.  202  and  203. 

The  suction-pump  theoretically  can  lift  water  through  34 
feet,  practically  through  about  28  feet;  that  is,  the  height 
of  a  column  of  water  which  the  atmosphere  will  sustain. 
Therefore  for  wells  deeper  than  28  feet  some  other  pump  must 
be  used.  In  Fig.  202,  C  represents  a  pipe  from  the  water  to 
the  top  of  a  well.  The  piston  A  has  a  valve  in  it  which  opens 

257 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


upward.  At  the  bottom  of  the  working-barrel  B  is  another 
valve  opening  upward.  When  the  piston  is  raised  a  is  opened 
and  b  is  closed,  a  volume  of  water  being  drawn  into  the  pipe 
equal  to  the  displacement  of  the  piston.  When  A  descends  b 


c 


D' 


Fie.  202.  FIG.  203. 

is  opened  -and  a  is  closed.  In  the  figure  the  piston  is  on  its 
upward  stroke.  This  is  the  form  used  with  the  old-style 
wooden  pump. 

Fig.  203  is  a  diagram  showing  the  principle  of  the  force- 
pump.      In  this  case,  a  solid  piston  is  used  having  no  valve  in 


PUMP1NG-MACHINER  Y. 


259 


it.  The  valves  are  shown  at  a'  and  V '.  On  the  up  stroke  a' 
is  opened  and  b'  is  closed.  On  the  down  stroke  a  is  closed 
and  b'  is  opened.  The  water  being  forced  out  by  the  piston 
or  plunger  through  the  pipe  D'  to  any  height,  depending  upon 
the  force  which  is  applied  to  the  piston.  Here  C'  must  not  be 
over  about  28  feet,  or  it  will  be  impossible  to  raise  the  water 


FIG.  204. 

to  the  pump-cylinder  by  means  of  suction.  This  form  requires 
a  much  stronger  construction  than  the  suction-pump,  owing  to 
the  increased  height  through  which  the  water  may  have  to  be 
raised.  It  is  evident  that  the  flow  of  water  from  the  delivery- 
pipe  D'  will  be  in  spurts  because  of  the  periodic  movement  of 
the  piston.  This  may  be  avoided  by  the  use  of  the  air-chamber 
placed  in  the  delivery-pipe  which  is  practically  an  enlargement 
of  the  delivery-pipe.  The  diagram  in  Fig.  204  shows  this 
arrangement,  which  is  identical  with  that  of  Fig.  203,  except 
for  the  addition  of  the  air-chamber  E.  When  water  is  forced 


2UO 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


into  E  the  air  is  compressed  so  that  after  a  few  strokes  the 
water  begins  to  issue  from  G  in  a  steady  stream,  being  forced 
from  the  air-chamber  by  the  compressed  air,  during  the  interval 
between  the  strokes  of  the  pump. 

These  diagrams  mentioned  heretofore  are  all  single  acting. 
Fig.  205  shows  a  double-acting  pump-piston.  As  has  been 
stated  before,  suction-pumps  are  used  only  for  lifting  water  or 
other  fluids  through  small  heights,  usually  for  drawing  water 
from  shallow  wells.  For  all  cases  in  which  the  fluid  is  to  be 


FIG.  205. — The  Deane  Double-acting  Force-pump. 

raised  to  great  heights  or  against  great  pressures  the  force- 
pump  is  used. 

The  manner  of  giving  motion  to  the  water-piston  is  differ- 
ent for  different  pumps,  but  steam  is  the  most  common  method 
of  supplying  the  force,  that  is,  a  steam-engine  is  used.  The 
following  is  a  classification  of  modern  pumps.  First,  according 
to  the  height  of  the  pump  above  the  water-supply:  Suction- 
and  force-pumps.  Second,  according  to  the  means  of  giving 
motion  to  the  water-piston : 

single. 
Steam-pumps  -  compound. 

duplex. 


PUMPJNG-M/iCHINERY.  261 

single. 

Power-pumps  -{  j-  Belted  or  Geared. 

triplex. 

centrifugal. 

Electric  pumps. 

Hot-air  pumps. 

Gas-pumps. 

Hydraulic  pumps. 

Windmill-pumps. 

In  the  steam-pump  one  or  more  steam-cylinders  are  used 
containing  a  reciprocating  piston,  operated  by  a  slide-valve. 
A  single  steam-pump  is  one  having  one  steam-cylinder  and 
one  water-cylinder.  A  compound  steam-pump  is  one  having 
two  steam-cylinders  (as  in  a  compound  engine)  driving  a 
water-piston. 

A  duplex  pump  is  one  having  two  single  pumps  side  by 
side  on  the  same  bed  delivering  into  a  common  pipe  and 
usually  supplied  by  a  common  suction-pipe.  In  this  construc- 
tion the  two  steam-pistons  usually  move  in  opposite  directions, 
so  that  the  slide-valve  for  one  steam -cylinder  may  get  its 
motion  from  the  piston-rod  of  the  other  by  means  of  suitable 
connection,  the  D-valve  always  moving  in  a  direction  opposite 
to  that  of  its  piston . 

Power-pumps  are  not  connected  direct  to  the  source  of  the 
power  but  are  connected  to  a  revolving  shaft  by  belts  or  gear- 
ing, this  shaft  receiving  its  motion  from  some  motor  separate 
from  the  pump.  Power-pumps  are  single,  duplex,  or  triplex, 
according  to  the  number  of  water-pistons. 

Electric  pumps  are  those  driven  by  electric  motors.  The 
high  speed  of  the  motor  is  reduced  to  the  slow  speed  required 
by  the  water-piston  by  means  of  gear-wheels. 

Gas-engines  are  sometimes  the  means  of  running  pumps. 
Again  as  with  electric  pumps,  the  high  speed  of  the  gas-engine 
is  reduced  to  the  necessary  slow  speed  of  the  pump  by  means 
of  gear-wheels  or  belts. 

A  hydraidic  pump  is  similar  to  the  steam-pumps,  with  the 


262 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


exception  that  water  at  a  great  pressure  is  used  as  the  motor- 
power  instead  of  steam.  In  fact,  some  of  the  steam-pumps  with 
slight  alterations  may  be  used  as  hydraulic  pumps.  This 
arrangement  is  practicable  only  where  a  large  amount  of 
water  is  at  hand  and  at  a  high  pressure,  due  to  natural 
causes. 

The  pumps  included  in  the  above  classification  are  not 
necessarily  water-pumps.  They  may  be  used  in  pumping  any 
liquid.  Petroleum  is  an  example  of  a  fluid  other  than  water 
which  is  pumped  through  long  lines  cf  piping  by  means  of 
these  various  pumps. 

Nearly  all  the  pumps  driven  by  steam  or  other  power 
are  force-pumps.  The  pumps  referred  to  in  the  following 
pages  will  be  force-pumps  unless  it  is  expressly  stated  other- 


wise. 


Power-pumps  are  fitted  either  with  pistons  or  plungers  in 


PLUNGER  AND  RING  PATTERN 


FIG.  206. — Single  Steam-pump. 

their  water-cylinders.  A  plunger  is  in  the  form  of  a  solid  rod, 
suitably  packed,  while  a  piston  is  more  in  the  shape  of  a  disk. 
A  plunger  is  shown  in  the  pump  in  Fig.  207. 

Fig.  206  shows  a  double-acting  single  pump  as  manufac- 


PUMPING-MACHINERY.  263 

tured  by  the  Worthington  Hydraulic  Works.  The  supply  of 
water  enters  through  C,  and  is  delivered  through  D.  The 
pump-piston  is  shown  at  B  "working  in  a  bored  ring.  The 
piston  is  made  somewhat  longer  than  the  stroke.  The  dis- 
charge-valves, near  Dy  open  upwards  and  consist  of  brass  disks 
held  down  by  springs.  The  supply-  or  suction-valves,  near 
Cy  also  open  upwards.  To  show  the  operation  of  pumping, 
suppose  the  piston  B  makes  a  stroke  toward  the  right.  The 
left-hand  suction-valve  will  be  opened  by  the  suction  and  the 
left-hand  discharge-valve  will  be  closed  by  means  of  the  ten- 
sion of  its  spring  as  well  as  the  pressure  of  the  water  above  it. 
Likewise  the  right-hand  suction-valve  will  be  closed  and  the 
force  of  the  plunger-stroke  will  cause  the  right-hand  discharge- 
valve  to  open  and  discharge  an  amount  of  water  equal  to  the 
displacement  of  the  piston.  From  this  point  it  passes  through 
the  air-chamber  and  out  through  the  discharge-pipe  in  a  steady 
stream.  The  steam  part  of  the  pump  is  made  plain  by  the 
drawing.  The  steam-piston  is  on  the  same  piston-rod  with 
the  water-piston.  Its  motion  is  controlled  by  the  D-valve  E. 
The  D-valve  is  connected  by  a  valve-rod  and  small  arms  to 
an  arm  F  which  swings  with  the  stroke  of  the  piston.  This 
arrangement  takes  the  place  of  the  eccentric  in  the  steam- 
engine,  necessarily  by  reason  of  the  fact  that  there  is  no  rotary 
motion  of  a  shaft  in  pumps  to  which  an  eccentric  could  be 
attached.  This  type  is  designed  for  light  service  such  as  filling 
railroad-tanks,  oil-tanks,  etc.  Fig.  207  shows  the  construc- 
tion of  a  pump  designed  for  heavy  pressures  such  as  are 
necessary  for  hydraulic  machinery,  as  hydraulic  cranes,  cotton 
presses,  hydraulic  riveting-  and  punching-machines,  and 
hydraulic  presses  of  all  kinds,  where  high  pressures  are 
required.  It  is  of  the  duplex  type  and  differs  from  the  pump 
shown  in  Fig.  206  mainly  in  that  it  has  water-plungers  instead 
of  pistons,  the  plungers  entering  the  cylinder-head  full  size  and 
being  made  of  brass.  There  are  four  single-acting  plungers, 
two  of  them  shown  in  the  cut,  and  the  other  two  behind  them, 
excluded  from  view  in  the  drawing.  The  pressure  which  this 


264 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


PUMPING-MACH1NER  Y. 


20=: 


pump  is  capable  of  producing  depends  mainly  upon  its  speed. 
The  reason  for  making-  the  plungers  single-acting  is  that  by 
dividing  the  work  done  between  four  plungers  instead  of  two 
the  strain  on  each  piece  is  made  less  and  hence  the  pieces 
may  be  made  lighter.  In  this  way  large  pressures  are  carried 


by    a 
ones. 


FIG.  208.  —  Power  pump, 
number    of   small    parts  rather    than   by    a  few    heavy 


It  has  just  been  stated  that  the  water-pressure  which  is 
maintained  by  the  pressure-pump  just  described  depends  largely 
upon  the  speed  of  the  pump.  This  would  naturally  cause  the 
pressure  to  be  very  uncertain  as  far  as  regularity  is  concerned. 
In  hydraulic  plants  also  where  hydraulic  machines  draw  off 


266 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


water-pressure   sometimes  at   irregular  intervals  the  pressure 
in  the  pump  delivery-pipe  is  very  irregular. 

For  the  purpose  of  giving  a  uniform  pressure  the  steam- 


accumulator  shown   in   Fig,    210  is  used  in   connection   with 
pressure-pumps. 

It  consists  of  a  large  steam-cylinder  in  which  the  piston  A 
works,  into  which  the  steam  from  the  boiler  enters  as  shown. 


PUMPING-M4CHINER  Y. 


267 


268 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


The  supply-steam  for  the  pump,  which  is  not  shown  in  the 
cut,  passes  from  the  steam-cylinder  of  the  accumulator  through 
the  perforations  in  the  pipe  C  and  out  at  D.  The  end  E  of 
the  accumulator  is  in  direct  connection  with  the  delivery-pipe 
of  the  pump.  F  \s  a  ram  which  is  bolted  to  the  piston  A  and 
moves  with  it,  passing  through  two  stuffing-boxes,. one  in  the 
steam  cylinder-head  and  one  in  the  ram  cylinder-head.  The 
perforated  regulating-pipe  C  is  stationary  and  enters  through 
the  piston  A  and  into  the  ram.  When  the  piston  A  moves  to 


FIG.  211. — Accumulator  and  Pump. 

the  left  it  covers  the  holes  in  C.  To  explain  the  regulation 
of  the  steam-supply  to  the  pump  in  order  to  meet  the  varia- 
tions of  consumption  we  will  suppose  that  the  pump  has  been 
running  fast,  causing  the  pressure  in  the  delivery-pipe  to  rise ; 
the  high  pressure  of  water  at  E  causes  the  ram  and  steam - 
piston  to  move  to  the  left.  This  causes  a  number  of  holes  in 
C  to  be  closed,  thereby  decreasing  the  quantity  of  steam 


PtfMPlNG-MACHINER  Y.  269 

admitted  to  the  pump  and  slowing  its  speed.  If  the  water- 
pressure  is  very  great  the  piston  A  will  be  pushed  far  enough 
to  cover  all  the  perforations  in  C  and  thereby  stop  the  pump 
entirely.  When  the  pressure  at  E  begins  to  fall,  due  to  the 
slowing  up  of  the  pump  or  to  the  drawing  off  of  water  by  some 
machine,  the  ram  and  piston  move  to  the  right,  uncovering 
the  perforations,  so  that  steam  is  admitted  to  the  pump,  thus 
increasing  the  speed  according  to  the  requirements  of  the 
service.  Fig.  211  shows  an  accumulator  of  this  type  built  in 
connection  with  a  pressure-pump. 

Figs.  212   and   213  show  a  plan  often  used  in  deep  water- 
wells,  in  which  the  water  fails  to  flow  to  the  surface  of  the 
ground.      It  consists  of  a  vertical  steam-engine  placed  directly 
over  the  top  of  the  well   and   a  single-acting  vertical  pump 
placed  in  the  well  at  such  a  depth  that  the  plunger  is  sub- 
merged or  within  suction  distance  of  the  water.      The  plunger 
is  attached  to  the  piston-rod  by  means  of  a  rod  made  up  of 
sections.      In  Fig.  212  A  is  the  steam-cylinder  containing  a 
reciprocating  piston,  B  is  the  steam-chest,  C  is  the  piston-rod, 
and  D  the  valve-rod,      a  b  is  a  rocker-arm  pivoted  at  e.      The 
end  b  is  attached  by  means  of  a  short  link  to  the  piston-rod 
at  c.      The  end  a  is  attached  directly  to  the  valve-rod.     When 
the  piston  makes  a  stroke  in  one  direction  this  arrangement 
causes  the  valve  to  move  in  an  opposite  direction ;  E  is  the 
discharge-pipe.       The    steam    from    the    boiler    enters    at    F. 
Fig.  213  shows  an  enlarged  view  of  the  water-plunger  and  the 
working-barrel.      AB  is  the  plunger  to  the  top    of  which  is 
attached  the  pump-rod.      It  works  in  a  brass  cylinder  D  which 
is  fastened  to  the  casing  of  the  well  and  which  is  called  the 
working-barrel.     E  is  called  the  foot-valve.      It  is  fastened  to 
the  bottom  of  the  working-barrel.      The  valves  in  the  foot- 
valve  and  the  plunger  consist  of  metal  balls  which  are  seated 
in  corresponding  openings  in  the  seats.      When  the  plunger 
makes  an   upward    stroke,    water   is    drawn  through  the  foot- 
valve,  the  ball  being  raised.      At  the  same  time  the  valve  in 
the    plunger    is    closed,  raising  the  water  above  it.      On    the 


27°  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC.  * 


1 

FIG.  212. 


FIG.  213. 


fUMPING-MACHINER  Y. 


271 


downward  stroke  the  foot-valve  is  closed  and  the  plunger*, 
valve  is  opened.  The  discharge-pipe  E  may  or  may  not  pass 
through  an  air-chamber. 


I 


Fig.  214  is  an  illustration  of  another 
method  of  raising  water.  It  is  called  tJie 
air-lift  method.  It  consists  of  a  vertical 
pipe  with  its  lower  end  submerged  in  the 
fluid  that  is  to  be  raised  and  a  smaller 
pipe  delivering  air  into  it  at  the  bottom. 
This  jet  of  air  carries  up  a  column  of  water 
mixed  with  air-bubbles.  The  air-pressure 
for  this  process  is  furnished  by  an  air-com- 
pressor which  pumps  the  air  into  a  receiver 
which  maintains  the  desired  pressure.  The 
air  is  taken  from  the  receiver  as  needed. 
The  height  to  which  the  water  is  lifted 
depends  upon  the  air-pressure  which  is  fur- 
nished by  the  compressor. 

Speed.- — Pumping-engines,  owing  to  the 
weight  of  the  water  and  its  incompressibility, 
cannot  be  run  at  the  high  speed  commonly 
given  to  steam-engines.      A  piston  speed  of 
about  100  feet  per  minute  is  commonly  made 
in  practice.    For  a  piston  with  a  1 2-inch  stroke 
FIG.  214.— Air-lift,    this  would  give  50  double  strokes  per  minute. 
Area    of   Water- valves. — The    water- valves    of    a    pump 
should  be  made  amply  large  so  that  the  velocity  of  the  water 
in  passing  through  them  will  not  be  too  great.      They  should 


272 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


have  an  area  large  enough  to  permit  the  passage  of  water 
through  them  at  a  rate  of  not  over  250  feet  per  minute.  The 
water-valve  is  usually  made  of  a  rubber  disk  or  of  composition 
brass  which  is  held  upon  its  seat  by  a  coil -spring. 

Water-piston.  —  Water-pistons  are  made  tight  usually  by 
hemp  or  other  fibrous  packing.  The  fact  that  most  water- 
pistons  are  constantly  in  contact  with  water  also  insures  their 
proper  working  and  lubrication.  They  are  often  made  of 
brass  in  order  better  to  stand  the  wearing  and  decomposing 
effect  of  different  kinds  of  water. 

Cylinders. — For  the  pressure  carried  in  high-pressure 
pumps  it  is  necessary  to  make  the  cylinder-walls  comparatively 
thick.  A  brass  lining  is  often  used  also,  which  is  better 
adapted  for  contact  with  water  than  is  iron. 

Government. — Ordinary  steam-pumps,  of  which  Fig.  206 
is  a  type,  are  governed  usually  by  hand,  by  throttling  the 

steam  with  the  steam-valve  at  the 
entrance  to  the  steam-chest.  The 
speed  is  too  slow  to  make  an 
accurate  centrifugal  governor. 
Fig.  2 1 5  is  a  sectional  cut  of  the 
Mason  Pump-governor.  It  con- 
sists mainly  of  a  cylindrical  shell, 
or  reservoir,  filled  with  oil  or 
glycerine.  The  plunger  A  A  is 
connected  through  the  arm  /  to 
some  reciprocating  part  of  the 
pump  or  engine,  and  works  in 
unison  with  the  strokes  of  the 
pump,  thereby  drawing  the  oil  up 
through  the  check-valves  DD  into 
the  chambers  JJ,  whence  it  is 
forced  alternately  through  the 
FIG.  2i5.-Mason  Pump.  passages  BB,  through  another  set 
governor.  of  check-valves  into  the  pressure- 

chamber  EE.      The  oil  then  returns  through  the  orifice  C,  the 


PUMPIN  C-MACHINER  Y.  273 

size  of  which  is  controlled  by  a  key  inserted  at  N,  into  the 
lower  chamber,  to  be  repumped  as  before.  In  case  the  pump 
or  engine  works  more  rapidly  than  is  intended,  the  oil  is 
pumped  into  the  chamber  EE  faster  than  it  can  escape  through 
the  outlet  at  C  ,  and  the  piston  GG  is  forced  upward,  raising 
the  lever  L  with  its  weight  and  throttling  the  steam.  In  case 
the  pump  runs  slower  than  is  intended,  the  reverse  action  takes 
place  ;  the  weight  on  the  end  of  the  lever  L  forces  the  piston 
GG  down  and  more  steam  is  let  on.  As  the  orifice  at  C  can 
be  increased  or  diminished  by  adjusting  the  screw  at  Ny  the 
governor  can  be  set  to  maintain  any  desired  speed.  The 
piston  GG  fits  over  the  stationary  piston,  forming  an  oil  dash- 
pot,  thereby  preventing  fluctuation  of  the  governor.  This 
dash-pot  is  fed  from  pressure-chamber  E  through  a  passage 
which  is  controlled  by  an  adjusting-screw  T,  which  is  set  by 
a  screw-driver  (after  removing  the  cap-screw  K}.  It  requires 
no  further  attention  after  once  adjusted. 

Water-  pressures.  —  A  pressure-gauge  similar  to  that  used 
for  steam-pressures  is  used  to  show  the  pressure  of  water. 
Fig.  216  shows  a  combination  water-pressure  gauge,  having 
two  sets  of  graduations,  one  showing  the  pressure  per  square 
inch;  the  other  showing  the  height  of  water  in  feet.  This 
gauge  may  be  placed  in  any  pipe  having  water-pressure  or  on 
a  tank,  stand-pipe,  or  reservoir. 

Capacity.  —  A  water-lifting  arrangement  is  usually  rated 
according  to  the  number  of  gallons  it  will  lift  in  unit  time,  and 
not  by  horse-power,  though  of  course  the  horse-power  could 
easily  be  calculated.  To  find  the  number  of  gallons  pumped 
per  hour  multiply  the  displacement  of  the  piston  per  stroke  in 
cubic  feet  by  the  number  of  strokes  per  hour,  and  by  7.48,  the 
number  of  gallons  in  a  cubic  foot.  Let  5  be  the  stroke  in  inches, 
A  the  area  of  the  piston  in  square  inches,  and  Arthe  number  of 
strokes  per  minute.  Then  the  capacity  in  gallons  per  minute  is 
SAN 


This  is  the  theoretical  capacity  made  upon  the  assumption 


274 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


that  at  each  stroke  a  quantity  of  water  is  pumped  equal  to  the 
displacement  of  the  piston  or  plunger,  and  allowing  nothing 
for  leakage.  The  length  of  the  stroke  varies  constantly,  also, 


FIG.  216. — Pressure-gauge. 

which  would  vary  the  quantity  of  water  pumped  in  a  given  time. 
Meter. — The  actual  volume  of  water  pumped  may  be 
measured  by  a  water-meter,  shown  in  Fig.  217-  It  is  placed 
so  that  the  water  discharged  by  the  pump  passes  through  it. 
It  is  used  in  any  place  where  water-supply  or  consumption  is 
to  be  measured.  The  internal  arrangement  of  the  Worthing- 
ton  meter  is  shown  in  longitudinal  section  in  Fig.  217  and  in 
transverse  section  in  Fig.  218.  The  plungers  A  A  are  closely 
fitted  in  parallel  rings.  The  water  passes  through  the  inlet 
and  port  /,  and  is  admitted  under  pressure  into  the  chamber 
D,  at  one  end  of  each  plunger  alternately,  while  the  connec- 
tion is  made  between  the  chamber  at  the  other  end  of  the  outlet, 
Thus  the  plunger  in  moving  displaces  its  volume,  discharging 
it  through  its  outlet.  The  arrangement  is  such  that  the  stroke 


PUMPING-MACHINER  Y. 


275 


FIG.  217. — Water-meter. 


FIG.  218. 


276  PUMPS,  GAS-ENGINES,  WATER  POWER,  ETC. 

of  the  plungers  alternate,  the  valve  actuated  by  one  admitting 
water  to  the  other.  The  plungers  are  brought  to  rest  at  the 
end  of  the  stroke  by  the  rubber  buffets  EE.  One  plunger 
imparts  a  reciprocating  motion  to  the  lever  F,  which  operates 
the  counter  mechanism  through  the  spindle-  and  ratchet-gear 
as  shown.  Thus  it  will  be  seen  that  the  counter  is  arranged 
to  move  the  dial-pointers  once  for  every  four  strokes  or  dis- 
placements, and  that  water  cannot  pass  through  the  meter 
without  registration,  for,  in  order  to  pass  through,  it  must  dis- 
place the  plungers,  and,  therefore,  be  recorded  by  the  move- 
ment of  the  lever  and  counter  mechanism ;  nor  can  there  be 
an  over-registration,  because  the  plungers  cannot  move  unless 
the  fluid  is  displaced. 

Duty. — The  duty  of  a  pumping-engine  means  the  number 
of  foot-pounds  of  work  done  by  the  pump  for  every  100  Ibs.  of 
coal  burnt  in  the  boiler-furnace.  It  is  practically  the  same  as 
"  efficiency." 

To  find  the  * '  duty  ' '  as  defined  above : 

Let  P  be  pressure  of  water  in  pounds  per  square  foot  in  the 
supply-pipe  of  the  pump  just  before  entering  the 
cylinder,  determined  by  multiplying  the  pressure- 
gauge  reading  by  144; 

Pl  be  the  pressure  of  water  in  pounds  per  square  foot 
in   the  discharge-pipe   as   the   water   leaves   the 
cylinder,  ascertained  as  before; 
h  =  difference  of  level  between  the  above  two  gauges 

in  feet; 

W=  weight  of  steam  used  per  hour  in  pounds; 
iv  —  weight  of  coal  burned  per  hour  in  pounds ; 
Q  =  number  of  cubic  feet  of  water  pumped  per  hour. 
The  head  of  water  h  may  be  reduced  to  pounds  per  square 
foot  by  multiplying  by  62.4,   the  weight  of  a  cubic   foot  ol 
water. 

Then  the  total  pressure  of  water  per  square  foot  upon  the 
water-piston  = 


PUMPING-MACHINER  Y.  277 

Pl  —  P  representing  the  pressure  required  to  overcome  the 
friction  and  the  resistance  due  to  the  head  in  the  pump,  and 
Jt  X  62.4  a  small  pressure  which  is  due  to  the  difference  of 
level  of  the  gauges  and  which  has  to  be  added  ;  then 

{P.-P+^X  62.4)}(2 

is  the  number  of  foot-pounds  of  work  done  per  hour.  Dividing 
by  w  we  have 

(Pl-P  +  (A  X62.4)i| 

as  the  number  of  foot-pounds  done  for  every  pound  of  coal 
burned. 

The  "  duty  "  is  100  times  this,  by  the  definition  of  duty  = 


NOTE.  —  Q  =  XL  A,  in  which  N  —  number  of  strokes  per 
hour,  L  =  length  of  stroke  in  feet,  and  A  =•  area  of  piston  in 
square  feet.  Hence,  multiplying  by  Q  is  equivalent  to  multi- 
plying the  total  pressure  on  the  piston  by  the  distance  moved 
by  that  pressure  per  hour. 

A  high-duty  pumping-engine  is  one  which  gives  an  exceed- 
ingly high  number  of  foot-pounds  per  every  100  Ibs.  of  fuel 
burned.  This  is  attained  by  using  the  steam  expansively. 
That  is,  by  a  compound  or  triple-expansion  steam-end  which 
of  course  gives  a  higher  efficiency  than  with  a  single  steam- 
cylinder. 

The  Indicator. 

The  pressure  within  the  water-cylinder  of  a  pump  may  be 
obtained  as  with  the  steam-cylinder  with  the  Indicator.  Figs. 
219  and  220  are  facsimiles  of  cards  taken  from  a  small  pump 
of  the  type  shown  in  Fig.  206.  Fig.  220  was  taken  from  the 
water-cylinder  and  Fig.  219  from  the  steam-cylinder.  The 
difference  in  the  height  of  the  two  cards  is  due  to  the  fact  that 
the  scale  of  the  indicator-spring  on  the  steam-end  was  No.  36, 
while  that  of  the  water-end  was  No.  48. 


278  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

By  reference  to  the  steam-card  it  will  be  noticed  that  the 
steam  was  working  non-expansively,  that  is,  steam  entered 
the  cylinder  during  the  whole  stroke.  By  working  up  these 


FIG.  219. — Indicator-card  from  Water-cylinder  of  Pump. 


FIG.  220. — Indicat  jr-card  from  Steam-cylinder  of  Pump. 

two  cards  it  will  be  found  that  less  work  was  done  on  the 
water-piston  than  on  the  steam -piston.  This  difference  repre- 
sents the  work  lost  in  friction. 

PROBLEMS. 

1.  A  pipe  whose  cross-section  is  one  square  foot  extends  vertically 
100  feet  into  the  air.     What  is  the  total  pressure  on  the  bottom  of  the 
pipe  ?     What  is  the  pressure  per  square  inch  ? 

Note. — The  weight  of  a  cubic  foot  of  water  is  62.4  Ibs. 

2.  Find  the  pressure  per  square  inch  on  the  bottom  of  a  stand-pipe 
having  the  same  height  as  the  ^bove,  but  having  a  cross-section  of  20 
square  feet.     Compare  results. 

3.  At  the  sea-level  the  pressure  of  the  air  is  14.  ;  Ibs.      It  will  also 
support  a  column  of  mercury  29.92  inches  high  or  a  column  of  water 
34  feet  high.     Find  pressure  per  square  inch  due  to  a  column  of  mer- 
cury i  inch  high  and  a  column  of  water  i  foot  high. 


PUMP1NG-MACHINER  Y.  279 

4.  The  plunger  of  a  pump  makes   100  strokes  of  24  inches  per 
minute,  and  is   6   inches   in   diameter.     Find  the  number  of  gallons 
pumped  per  minute  and  per  hour. 

5.  Find  the  number  of  foot-pounds  of  work  done  per  hour  in  the 
above  if  the  water  is  pumped  into  a  tank  50  feet  above  the  water  source. 

6.  A  pump  discharges  100  cubic  feet  of  water  per  minute.     What 
should  be  the  area  of  the  two  discharge- valves  through  which  the  water 
passes  in  order  that  the  velocity  of  the  w^ter  through  them  shall  not  be 
more  than  250  feet  per  minute  ? 

7.  Sixty  cubic  feet  of  water  is  pumped  per  hour,  during  which  time 
15  Ibs.  of  coal  is  burned  in  the  furnaces  for  it.     The  pressure  in  the 
discharge-pipe  as   shown   by  the   pressure-gauge  is  90  Ibs.,  while  the 
pressure  in  the  suction-pip 3  is  zero,  and  the  two  gauges  are  on  the  same 
level.     Find  the  duty  of  the  engine. 

8.  Work  up  the  card  shown   in  Fig.  220,  and  find  the  indicated 
H.P.  of  the  steam-cylinder,  the  stroke  being  4^  inches,  the  diameter  of 
cylinder  5  inches,  and  making  40  strokes  per  minute. 

9.  Find  indicated  H.P.  of  water-cylinder,  stroke  4^  inches,  diam- 
eter of  cylinder  3T^,  and  40  strokes  per  minute. 

10.  Find  indicated  H.P.  lost  in  friction. 

11.  Determine  the  efficiency  of  the  pump. 


CHAPTER    XXIV. 


GAS-ENGINES. 

THE  Gas-engine  differs  from  the  steam-engine  in  that  the 
whole  process  of  transformation  of  the  heat-energy  of  the  fuel 
into  mechanical  work  is  carried  out  within  the  engine  itself. 
Gas  is  introduced  into  a  cylinder,  containing  a  piston ;  it  is 
compressed  and  then  ignited  or  exploded,  and  the  expansion 
of  the  gas  due  to  its  burning  gives  the  piston  a  forward  impulse. 

In  the  steam-boiler  furnace  it  is  necessary  to  give  air  to  the 
fuel  in  order  to  furnish  enough  oxygen  to  support  combustion. 
The  same  is  true  of  combustion  in  a  gas-engine.  A  certain 
quantity  of  air  is  mixed  with  the  gas  before  it  is  ignited  in  the 
cylinder.  If  the  chemical  constitution  of  a  gas  is  known,  the 
volume  of  oxygen  necessary  for  making  the  proper  explosive 
mixture  can  be  calculated. 

Pressures  and  Temperatures  of  Exploding  Gas. — With  a 
mass  of  any  perfect  gas  confined  within  a  closed  vessel  the 
absolute  temperatures  and  pressures  are  proportional  to  each 
other,  according  to  the  law  of  Charles. 

The  following  figures  are  the  results  of  experiments  by 
Dugald  Clerk  with  different  mixtures  of  coal-gas  and  air. 


Mixture. 

Maximum 
Pressure  above 
Atmosphere. 
Pounds  per 
Square  Inch. 

Temperature  of 
Explosion  calculated 
from  observed 
Pressure. 

Theoretical  Tem- 
perature of  Explosion 
if  all  Heat  were 
evolved. 

Gas. 

Air. 

vol. 

14  vols. 

40 

1483.8°  F. 

3237-  8«  F. 

13 

51-5 

1892.4 

3473-6 

12 

60 

2196.6 

3736-4 

II 

61 

2228 

4042.4 

9 

73 

2835.6 

4838 

7 

87 

3151-4 

6033.2 

6 

go 

3257.6 

6931.4 

5 

Qi 

3293.6 

4 

80 

2903 

280 


GAS-ENGINES.  281 

The  temperature  before  explosion  Was  30.6°  F. 

The  temperatures  in  the  fourth  column  are  derived  from 
the  law  of  Charles :  tht  volume  of  a  perfect  gas  at  a  constant 
pressure  is  proportional  to  the  absolute  temperature,  or  if  the 
volume  is  constant  the  pressure  is  proportional  to  the  absolute 
temperature  and  the  absolute  temperature  is  proportional  to 
the  pressure,  or 


A 


o» 


in  which  /t  is  the  absolute  temperature  corresponding  to  the 
pressure  pl ,  /0  is  atmospheric  pressure,  and  ^  =  491°,  the 
absolute  temperature  corresponding  to  32°  F.  The  figures  in 
the  fifth  column  are  those  that  would  be  obtained  theoretically 
if  all  the  gas  were  perfectly  burned,  the  volume  remaining 
constant,  and  there  being  no  loss  of  heat  by  conduction  into 
the  walls  of  the  cylinder.  The  fact  that  the  temperatures  due 
to  the  observed  pressures  are  so  much  lower  than  the  theoret- 
ical temperatures  indicates  that  the  combustion  is  not  perfect 
at  the  time  of  the  explosion,  when  the  maximum  pressure  is 
observed. 

From  the  above  table  we  find  that  coal-gas  will  give  tem- 
peratures of  explosion  of  from  1480°  F.  to  3300°  F.,  depend- 
ing upon  the  dilution  of  the  mixture.  It  is  also  seen  that  a 
mixture  of  I  vol.  of  gas  and  4  vols.  of  air  gives  a  lower 
pressure  than  a  mixture  of  I  vol.  of  gas  and  6  vols.  of  air. 
Gas  and  air  in  the  proportion  of  I  to  5  gives  about  the  maxi- 
mum pressure  when  coal-gas  is  used. 

CLASSIFICATION   OF    GAS-ENGINES. 

Modern  gas-engines  may  be  divided  into  two  great  classes, 
viz.,  those  in  which  the  piston*  receives  an  impulse  due  to  the 
explosion  of  gas  once  for  every  four  strokes,  that  is,  for  every 
two  revolutions,  and  those  in  which  the  piston  receives  an 
impulse  for  each  revolution  of  the  crank-shaft. 


282  PUMPS,  GAS  ENGINES,  WATERPOWER,  ETC. 

The  former  is  called  the  four-cycle  or  Otto  type;  Otto 
having  been  the  first  to  make  practical  engines  of  the  four- 
cycle type. 

The  latter  is  called  the  two-cycle  type.  It  is  now  rarely 
used. 

Most  gas-engines  are  single-acting. 

In  all  gas-engine  practice  it  has  been  found  that  the  highest 
efficiency  is  attained  by  compressing  the  gas  in  the  cylinder 
before  igniting  it.  In  some  early  engines  two  cylinders  were 
used,  one  of  which  was  used  for  compressing  the  gas,  which 
was  then  introduced  into  a  power-cylinder  and  suddenly 
ignited,  the  resulting  explosion  driving  the  piston  forward. 

The  Otto  type  uses  the  same  piston  for  compression  and 
for  power.  Its  operation  is  as  follows:  During  the  first  out- 
ward stroke  the  cylinder  is  charged  with  gas  and  air;  on  the 
first  inward  stroke  this  mixture  is  compressed.  At  the  begin- 
ning of  the  second  outward  stroke,  the  compressed  mixture  is 
ignited  and  the  piston  is  driven  forward.  During  the  second 
inward  stroke  the  burned  gases  are  exhausted  into  the  atmos- 
phere. 

Fig.  22 1  shows  a  sectional  plan  of  the  original  engine 
invented  by  Otto.  A  is  the  cylinder  which  is  closed  at  one 
end  only,  doing  away  with  the  stuffing-box  of  the  ordinary 
steam-engine.  B  is  the  piston  connected  directly  to  the  crank 
by  a  connecting-rod.  This  does  away  with  the  piston-rod  and 
cross-head  as  used  on  steam-engines.  C  is  the  compression- 
space  which  is  not  traversed  by  the  piston.  /  is  the  admission- 
and  ignition-port,  communicating  alternately  with  the  gas  and 
air  admission-port  K,  and  the  flame-port  L  in  the  slide  M. 
N  is  the  covering  holding  the  slide  to  the  cylinder-face  and 
carrying  in  it  an  external  flame  for  lighting  the  movable  one 
in  the  flame-port  L.  The  exhaust-valve  is  seen  at  O. 

P  is  the  cam-shaft  driven  by  the  use  of  bevel-gears  from 
the  crank-shaft,  which  operates  the  admission,  the  exhaust, 
and  the  igniting  apparatus.  To  start  the  engine  the  flame  at 
T  is  lighted;  the  cock  commanding  the  internal  flame  being 


GAS  ENGINES. 


283 


or   - 

UNIVERSITY  j 


284-  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

adjusted,  and  the  gas  turned  on,  a  couple  of  turns  at  the  fly- 
wheel, by  hand,  causes  ignition  and  sets  the  engine  in  motion. 
The  regulation  of  the  speed  of  the  engine  is  made  by  a 
centrifugal  governor  which  closes  the  gas-supply  when  the 
engine  speed  is  increased.  This  causes  an  explosion  to  be 
missed,  air  only  being  drawn  into  the  cylinder.  When  running 
without  load,  eight  or  more  revolutions  may  be  made  per 
explosion. 

Heaiy  Construction. 

Owing  to  the  fact  that  only  one  impulse  is  given  for  every 
two  revolutions,  it  becomes  necessary  with  engines  of  the  Otto 
type  to  make  all  the  parts  very  strong  in  order  to  withstand 
the  increased  shock  per  stroke. 

The  fly-wheel  is  also  made  very  large  in  order  to  carry  the 
engines  over  the  compression  stroke,  during  which  no  impulse 
is  made. 

The  objections  to  the  four-cycle  just  named,  that  is,  the 
heavy  construction  necessary,  have  caused  a  great  deal  of 
study  and  investigation  by  gas-engine  builders  in  producing 
engines  making  an  impulse  for  every  revolution. 

The  Day  gas-engine  showrn  in  vertical  section  in  Fig.  222 
may  be  taken  as  an  example  of  this  type. 

B  is  the  piston,  C  is  the  connecting-rod,  D  the  crank-pin. 

The  crank-shaft  operates  in  the  closed  chamber  E,  which 
chamber  serves  as  a  reservoir  for  gas  and  air  mixture. 

F  is  the  charge  inlet-port  which  admits  the  charge  of  gas 
and  air  to  the  cylinder.  G  is  the  exhaust-port,  allowing  the 
discharge  of  the  burned  gases. 

The  action  of  the  engine  is  as  follows:  On  the  up  stroke 
of  the  piston  B  the  pressure  of  the  gases  in  the  chamber  E  is 
reduced  to  a  little  less  than  atmospheric  pressure.  When  the 
piston  reaches  the  end  of  its  up  stroke,  the  air  inlet-port  H  is 
uncovered  by  the  lower  edge  of  the  piston  and  air  rushes  into 
the  chamber  E,  bringing  the  pressure  up  to  that  of  the  atmos- 
phere. 


G/tS-ENGINES. 


'85 


Gas  is  also  admitted  at  the  same  time  by  means  of  a  valve 
controlled  by  the  governor,  so  that  E  is  filled  with  a  mixture 
of  gas  and  air. 

On  the  down  stroke  of  the  piston  B  this  mixture  of  gas  and 
air  is  compressed  to  a  few  pounds  above  atmospheric  pressure 


FIG.  222. — Day  Engine. 

and  at  the  termination  of  the  stroke  the  port  F  is  uncovered 
by  the  piston,  causing  the  mixture  in  E  to  flow  into  the  top 
part  of  the  cylinder,  striking  against  the  baffle-plate  /,  which 
causes  it  to  flow  upward  and  then  downward,  as  shown  by  the 
arrow,  expelling  the  burned  gases  of  the  previous  stroke. 

When  the  piston  B  makes  its  next  upward  stroke,  it  com- 
presses this  mixture  into  a  small  space  at  the  end  of  the 
cylinder  to  a  pressure  of  about  50  Ibs.  above  atmospheric 
pressure. 


286  PUMPS,  GAS-ENGINES,  IV AT E'R- POWER,  ETC. 

At  this  point  the  hot-tube  L  ignites  the  compressed  mixture 
and  the  piston  makes  a  downward  stroke  due  to  the  impulse 
of  the  explosion.  By  this  arrangement  an  impulse  is  made  for 
each  revolution. 

The  disagreeable  noise  of  the  exhaust-discharge  is  averted 
by  conducting  it  first  to  an  exhaust-chamber  G2  and  then  to 
the  atmosphere  by  the.  pipe  Gy 

Owing  to  the  very  high  temperature  of  exploding  gases  it 
is  necessary  to  circulate  water  around  the  cylinder,  because  the 
cylinder-walls  would  be  so  highly  heated  that  the  entering  gas 
would  be  ignited  without  compression. 

Indicator-cards. — The  pressure  in  a  gas-engine  cylinder 
may  be  indicated  with  an  indicator  similar  to  the  steam-engine 
indicator,  but  a  very  strong  spring  must  be  used  in  order  to 
reduce  the  effects  of  inertia  due  to  the  shock  of  the  explosion. 

Fig.  223  shows  a  normal  diagram  of  the  work  in  a  gas- 
engine  of  the  Otto  or  four-cycle  type.  The  line  1-2  is  made 


1150  C. 


INS.  DlA.  CYLINDER.     14  INS.  STROKE. 
FIG.  223. 


120°  C. 

160  REVS.  PER  WIN. 


while  the  piston  draws  in  the  charge  and  shows  that  the  pres- 
sure falls  a  little  below  atmospheric  pressure,  which  is  due  to 
the  fact  that  the  admission-port  offers  resistance  to  entering 
air  and  gas. 

On  the  return  stroke  (first  instroke)  the  line  2  to  5  is  made, 
the  pressure  rising  by  compression  to  the  point  5,  at  which  point 


G/tS-ENGlNES.  2^7 

ignition  occurs  and  the  explosion  raises  the  pressure  suddenly 
as  shown  near  6. 

The  line  6-7  may  be  called  the  expansion-curve  (adiabatic 
expansion),  the  exhaust- valve  opening  at  7. 

On  the  second  return  stroke  the  exhaust  gases  are  expelled 
as  shown  by  the  line  8-1. 

The  gas-engine  indicator-card  will  not  as  a  usual  occur- 
rence be  as  regular  in  outline  as  the  one  just  shown,  because 
of  the  effects  of  the  inertia  of  the  parts  of  the  indicator.  A 

The  temperatures  of  the  working  mixture  during  the  cycle 
are  (for  convenience)  marked  upon  the  card.  The  formula  for 

PLAN 

the  H.P.  is  -        -  ,  in  which  the  factors  are  the  same  as  for  the 
33.000 

steam-engine,  remembering  that  X  will  be  the  number  of 
impulses. 

Losses  in  a  Gas-engine. — The  principal  losses  in  a  gas- 
engine  are:  1st,  heat  given  out  to  the  walls  and  the  jacket- 
water,  and  2d,  great  heat  expelled  in  the  exhaust  gases. 
These  losses  cannot  be  avoided  but  may  be  made  less  by  care- 
ful designing. 

The  following  is  the  result  of  a  test  and  calculation  made 
by  Thurston  upon  a  gas-engine,  which  represents  the  distribu- 
tion of  heat  in  good  gas-engines : 

Heat  transferred  into  useful  work,  17  per  cent. 

Heat  transferred  to  the  jacket- water,  52  per  cent. 

Heat  lost  in  the  exhaust  gas,   1 6  per  cent. 

Heat  lost  by  conduction  and  radiation,   I  5  per  cent. 

This  shows  an  efficiency  of  17  per  cent. 

The  Working  Fluid. — Any  fuel  that  is  not  in  the  gaseous 
state  already  may  be  converted  into  a  gas  suitable  for  use  in  a 
gas-engine. 

Generally  speaking,  the  amount  of  power  that  can  be 
derived  from  any  fuel  is  greater  when  it  is  first  made  into  a 
gas  and  then  used  to  drive  a  gas-engine,  than  when  the  fuel  is 
burned  in  the  furnace  of  a  steam-boiler  producing  power  for  a 
steam-engine. 


288 


PUMPS,  GAS-ENGINES,  WATER  POWER,  ETC. 


The  most  common  gas-fuel  is  city  ga«. 

The  amount  used  by  the  engine  is  measured  with  a  gas- 
meter. 

Gas-producing  plants  are  sometimes  arranged  which  manu- 
facture gas  for  the  direct  use  of  a  particular  gas-engine. 

Fig.  224  shows  such  an  apparatus  which  is  designed  to  use 
anthracite  coal.  The  producer  at  the  left  is  a  brick  chamber 
lined  with  fire-brick. 


FIG.  224. — Producer  Gas-plant. 

At  the  bottom  is  a  furnace  and  grate.  Coal  is  placed  in 
the  upper  part  and  the  heat  of  the  furnace  drives  off  the  vola- 
tile matter  in  the  form  of  gas,  smoke,  etc. 

From  the  top  of  the  producer  this  gareous  matter  is  carried 
by  a  pipe  to  the  bottom  of  the  scrubber.  This  scrubber  is 
filled  with  water  and  other  substances,  which  catch  all  the 
impurities  and  allows  pure  gas  only  to  reach  the  top. 

From  the  top  of  the  scrubber  the  gas  is'  carried  by  a  pipe 
to  the  holder,  which  is  sealed  with  water,  the  gas  being  above 
the  surface  of  the  water,  from  whence  it  is  taken,  as  needed, 
by  the  engine. 

VALVES    AND    VALVE-MECHANISMS. 

The  majority  of  modern  gas-engines  are  of  the  Otto  type 
and  the  admission-  and  exhaust-valves  are  poppet-valves  held 
upon  their  seats  by  a  spring  (see  Fig.  228).  These  valves  are 


GAS-ENGINES.  289 

operated  from  the  cam-shaft  by  means  of  cams,  levers,  etc. 
(see  Fig.  228).  The  cam-shaft  is  operated  by  the  crank-shaft 
by  means  of  bevel-gears,  the  axes  of  the  crank-shaft  and  cam- 
shaft being  perpendicular  to  each  other. 

REGULATION. 

There  are  two  general  methods  of  controlling  the  speed  of 
gas-engines  for  variable  loads.  1st,  by  varying"  tlie  number  of 
impulses,  which  is  called  the  hit-and-miss  method,  and  2d,  by 
varying  the  strength  of  tlie  impulse,  the  number  of  impulses 
being  the  same  for  each  revolution,  but  the  strength  of  the 
irr. pulse  being  varied  by  different  means. 

The  hit-and-miss  method  may  be  carried  out  in  three  ways: 

1st.  By  holding  the  gas- valve  closed  during  the  time 
required  for  one  or  more  impulses;  2d,  by  stopping  the  action 
of  the  exhaust-valve,  keeping  it  either  open  or  closed  during 
the  idle  strokes. 

When  the  exhaust-valve  is  held  open  the  suction  within 
the  cylinder  is  not  sufficient  to  open  the  admission-valve. 
When  the  exhaust-valve  is  kept  closed  during  the  idle  strokes, 
the  products  of  combustion  are  kept  in  the  cylinder,  which  of 
course  keeps  the  pressure  within  too  great  to  allow  an  admis- 
sion of  new  mixture. 

3d.    By  cutting  off  the  current  from  the  igniter. 

In  this  case  the  governor  is  attached  to  a  switch,  which  is 
opened  when  a  speed  is  reached  which  is  above  normal,  the 
charge  within  the  cylinder  being  alternately  compressed  and 
expanded  until  the  speed  is  decreased  to  normal  and  the  switch 
closed. 

The  variable-impulse  method  may  also  be  carried  out  by 
three  different  methods: 

1st.  By  reducing  the  proportion  of  gas  in  the  full  mixture, 
that  is,  by  a  partial  stoppage  of  the  gas-supply.  Of  course  if 
the  mixture  is  poor  in  gas  the  force  of  each  impulse  will  be 
correspondingly  small. 

2cl.    By  reducing  the  quantity  of  mixture  admitted  without 


290  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

altering  the  proportion  of  gas  and  air.  This  method  is  similar 
to  the  method  used  with  the  steam-engine  using  a  throttling- 
governor. 

3d.  By  varying  the  point  of  the  stroke  at  which  ignition 
occurs. 

The  greatest  strength  of  impulse  is  obtained  by  igniting  at 
such  a  time  that  the  maximum  pressure  is  at  the  beginning  of 
the  stroke. 

Making  the  ignition  earlier  or  later  than  this  will  decrease 
the  force  of  the  impulse  and  hence  the  speed. 

The  six  methods  above  named  are  operated  by  two  classes 
of  governors,  viz.,  the  centrifugal  governor  and  the  inertia 
governor.  The  centrifugal  governor  works  upon  the  same 
principle  as  that  used  on  throttling  steam-engines. 

Fig.  229  shows  an  example. 

Fig.  225  shows  one  form  of  the  inertia  governor  which  is 


FIG.  225. — Inertia  Governor.* 

used  only  with  the  hit-and-miss  method.  The  valve-stem  S 
is  operated  from  the  cam-shaft  by  means  of  the  slide  M. 

Every  time  M  strikes  5  the  valve  is  opened. 

To  the  slide  is  connected  the  pendulum  P,  which  swings 
about  a  pivot.  When  the  speed  is  above  normal,  the  pendulum 
lags  behind,  "causing  a  to  strike  the  pin  C,  which  causes  C  to 
catch  the  block  B  and  hold  the  valve  open. 

*  From  the  "Gas-engine  Hand-book  by  E.  W.  Roberts." 


GAS  ENGINES. 


291 


Fig.  226 


As  soon  as  the  speed  decreases  enough  the  arm  a  releases 
B,  so  that  the  exhaust-valve  is  closed  and  the  engine  admits 
fuel  for  another  impulse.  This  it  will  be  seen  is  that  method, 
already  described,  .in  which  the  exhaust-valve  is  kept  open 
during  the  idle  strokes. 

IGNITERS. 

There  are  four  ways  of  igniting  the  charge  in  a  gas-engine: 

1.  Ignition   by  means   of  a   naked  flame   as   in   the   Otto 
engine,  Fig.  221. 

2.  Contact  with  a  surface  which  is  at  a  high  temperature, 
as  shown  in  Fig.  222. 

The  hot-tube  is  the  best  example  of  this  class, 
shows  an  old  arrangement  of  this 
class. 

A  part  of  the  cylinder  is  shown 
at  the  right. 

The  \\rought-iron  tube  I  is 
heated  by  the  Bunsen  flame  2. 

The  piston  at  the  proper  time 
uncovers  the  hole  4,  and  the  mix- 
ture entering  under  pressure  is 
ignited. 

3.  Ignition  by   means    of  the 
flame  of  an  electric  arc.     With  this 
form  of  igniter  an  electric  circuit 
from  a  battery  is  closed,  by  means 
of  contact  points  which  are  situated 
within      the      compression-space. 
The  breaking  and  closing  of  the 
circuit  is  effected  by  means  of  cams 
or    eccentrics  and   links   operated 
from  the  cam-shaft. 

This  latter  method  of  ignition 
is  probably  the  most  popular 
method  in  modern  gas-  and  gaso- 
line-engines. 


FIG.  226.  — Hot-tube. 


29  2 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


GASOLINE-ENGINES. 

The  gasoline-engine  is  practically  the  same  as"  the  gas- 
engine  except  for  a  few  details,  and  many  engines  are  manu- 
factured which  may  be  used  either  for  gas  or  for  gasoline. 

Gasoline  is  introduced  into  the  cylinder  in  a  finely  divided 
spray  by  passing  a  jet  of  air  over  the  gasoline  as  it  enters. 
This  spray  is  then  compressed  and  ignited  just  as  if  it  were  a 
mixture  of  air  and  gas. 

The  gasoline  is  supplied  to  the  engine,  from  a  tank  placed 
below  it,  by  means  of  a  gasoline-pump,  which  pump  is  operated 
from  the  cam-shaft  by  suitable  gearing.  The  other  details  of 
gasoline-engines  are  practically  the  same  as  for  gas-engines. 
Fig.  227  shows  the  general  arrangement  of  the  engine  and 


FIG.  227. — Arrangement  of  Engine  for  using  Gasoline. 

gasoline-tank  for  a  stationary  plant.  T  is  the  gasoline-tank, 
P  is  the  gasoline-pump,  and  5  is  the  pipe  leading  to  the  pump 
from  the  tank. 

The  pump  lifts  the  gasoline  from    the   tank   through   the 


GAS-EHG1NFS. 


supply-pipe  ^>  into  the  overflow-cup  A',  containing  about  £  to 
£  pint  according  to  the  size  of  the  engine.      From  the  cup  the 


FIG.  228.— Cylinder  and  Governing  Device  of  the  Otto  Gasoline-engine. 

gasoline  is  admitted  through   the    gasoline-valve    V  into  the 
mixing  valve  of  the  engine.      By  means  of  the  overflow-cup  N 


FIG.  229. 

and  the  overflow-pipe  O  the  over-supply  of  gasoline  which  the 
pump  is  capable  of  supplying  is  taken  back  to  the  tank.     When 


-94 


PUMPS,  GAS-ENGINES,  WATER  POWER,  ETC. 


starting  the  engine  it  is  necessary  to  pump  gasoline  into  the 
cup  N  by  hand. 

This  is  done  by  means  of  the  hand-lever  K,  which  is  dis- 
connected from  the  engine  by  unscrewing  the  pin  M.  Fig. 
228  shows  an  end  view  and  Fig.  229  a  side  view  of  the 
cylinder  and  governing  apparatus  of  the  Otto  gasoline-engine. 

OIL-ENGINES. 

The  oil-engine  may  be  taken  as  another  type  of  the  gas- 
engine  in  which  another  step  is  added  to  the  process  already 
described  for  the  gasoline-engine,  of  atomizing  the  fuel  by  a 
jet  of  air. 

In  the  oil-engine  the  fuel,  which  is  oil,  is  not  only  first 
atomized  by  the  process  already  described,  but  it  is  vaporized 
by  passing  it  through  a  heated  chamber. 

By  these  two  operations  the  oil  is  converted  into  a  gas,  after 
which  it  is  introduced  into  the  cylinder,  compressed,  and 
ignited  as  in  the  gas-engine. 

The  atomizing  principle  rs  best  shown  by  the  perfume 
spray-producer  shown  in  Fig.  230. 


FIG.  230.— Perfume-sprayer. 

In  this  elementary  form  an  air-blast  passing  from  the  small 
jet  A  crosses  the  top  of  the  tube  B  and  creates  a  partial  vacuum 
within. 

The  liquid  in  the  bottle  then  flows  up  the  tube /?and,  issuing 
at  the  top  through  a  small  orifice,  is  blown  into  a  fine  spray. 


G/tS-ENGINES. 


295 


This  principle  is  used  for  spraying  gasoline  and  oil.  In 
the  oil-engine  this  spray  is  then  easily  vaporized  by  heat  and 
then  introduced  into  the  engine.  The  principal  fuel  used  in 
oil-engines  is  petroleum.  Fig.  231  shows  a  very  simple 


FIG.  231. 

vaporizing  arrangement  for  oil-engines  as  used  on  the  Hornsby- 
Ackroyd  oil-engine.  Vaporizing  is  done  by  introducing  the 
spray  into  the  combustion-chamber  A,  which  is  arranged  so 
that  the  heat  of  each  explosion  maintains  it  at  a  temperature 
high  enough  to  vaporize  the  spray  by  mere  injection  upon  the 
hot  surfaces,  the  heat  being  sufficient  to  ignite  the  mixture  of 
vapor  and  air  when  it  is  compressed.  To  start  the  engine,  the 
vaporizer  is  first  heated  by  a  separate  lamp,  the  spray  is 
injected  into  the  inlet  B,  and  the  engine  is  given  a  few  turns 
by  hand,  after  which  the  heat  of  each  explosion  furnishes  heat 
for  vaporizing  the  charge  for  the  next  impulse. 

Fig.  232  shows  a  section  through  the  vaporizer  and  cylin- 
der of  the  Priestman  oil-engine.  K  is  the  cylinder  and  E  is 
the  vaporizer. 

The  oil  is  sprayed  and  forced  into  R  by  means  of  an  air- 
pump  which  is  operated  by  the  cam-shaft.  The  vaporizer  is 
kept  hot,  while  the  engine  is  running,  by  the  exhaust  gases 
which  leave  the  cylinder  through  the  exhaust-valve  N  and  the 
port  O,  entering  the  jacket  P  which  surrounds  the  vaporizer. 

The  oil-engine  is  not  as  economical  in  the  use  of  fuel  as 
the  gas-  or  gasoline-engine ;  and  besides  this  it  is  difficult  to 


296 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


design  them  so  that  there  is  no  danger  of  explosion  without 
making  them  very  uneconomical  as  far  as  converting  heat- 
units  into  useful  work  is  concerned. 


H 


FIG.  232. 

The  jacket- water  for  gas-,  gasoline-,  and  oil-engines  is 
supplied  by  means  of  a  water-pump  usually  operated  from  the 
cam-shaft. 


CHAPTER  XXV. 
WATER-POWER. 

WATER-MOTORS  are  those  in  which  the  working  fluid  is 
water,  corresponding  to  steam  in  the  steam-engine  for  pro- 
ducing motion.  The  pump  does  not  belong  to  this  class, 
being  an  instrument  which  acts  upon  water  rather  than  one 
upon  which  water  acts.  Water  is  practically  incompressible 
and  consequently  inexpansible,  hence  it  cannot  be  used 
expansively  in  water-engines,  as  is  the  case  with  steam,  though 
water  is  sometimes  used  in  engines  similar  to  those  which  use 
steam  for  the  working  fluid.  Hence  an  indicator-card  taken 
from  a  reciprocating  water  or  hydraulic  engine  would  show  a 
maximum  pressure  line  approximately  parallel  to  the  atmos- 
pheric line. 

In  the  steam-engine  the  pressure  of  steam  depends  upon 
the  quantity  of  heat  supplied  to  it  in  the  boiler. 

Water-pressure  depends  upon  the  height  of  its  source  and 
its  velocity.  Here  the  term  "head"  is  used  instead  of  height 
in  calculating  water-pressure;  that  is,  we  say  that  a  head  of 
50  feet  is  obtained  from  a  natural  stream  when  its  source  is 
50  feet  above  where  its  water  is  applied  to  the  motor. 


V  =  V2gH, (i) 

is  an  equation  connecting  head  and  velocity,  in  which  V  is 
velocity  in  feet  per  second,  //the  head  in  feet,  and  g  —  32.2 
The  head  H  in  feet  may  be  reduced  to  pounds  per  square 
inch  by  multiplying  by  62.4  the  weight  of  a  cubic  foot  of  water 
and  dividing  by  144.     This  is  equivalent  to  multiplying  the 

62.4 

head  in  feet  by  — — —  =  .426. 
144 

297 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


The  head,  instead  of  being  an  actual  distance  between 
levels,  may  be  caused  by  pressure  as  by  a  pump.  A  pressure- 
gauge  may  be  used  for  reading  this  pressure  or  head. 

The  two  terms  pressure  and  head  are  often  used  one  for 
the  other. 

There  are  two  general  classes  of  water-motors,  viz. :  Those 
having  rotary  pistons  or  runners  and  those  having  reciprocating 
pistons.  The  former  are  by  far  the  more  common  in  American 
practice. 

The  following  is  a  classification  of  the  principal  water- 
motors  : 

f  Overshot  wheel. 
Water-wheels  4  Undershot  wheel. 


I.   Rotary  - 


(  Breast-wheel, 
f  Parallel  flow. 

~    ,  .  T>    j-  i  n          (  Outward. 

Turbines  -{  Radial  now    J 

( Inward. 

[Mixed  flow. 
(  Impulse. 

Uet. 
2.   Reciprocating  Hydraulic  Engines. 


Motors 


FIG.  233. 

The  simplest  and  first  used  of  the  water-motors  is  the 
water-wheel,  in  which  the  water  produces  motion  by  acting1 
directly  against  vanes  or  buckets  placed  upon  the  circumfer- 
ence of  a  wheel.  Fig.  233  shows  an  overshot  wheel. 


WATER-POWER. 


299 


The  circumferential  speed  of  the  wheel  will  be  the  same  as 
the  velocity  of  the  water,  which  from  (i)  is  V  =  V2gH,  H  being 
the  head.  If  this  velocity  in  feet  per  second  be  multiplied  by 
the  pressure  on  the  vane  due  to  the  weight  of  the  water,  we 
have  the  foot-pounds  of  work  done.  Suppose  that  the  cross- 
section  of  the  stream  of  falling  water  is  B  square  feet;  then 
B  ^2gH  cubic  feet  is  the  volume  and  its  weight  is  62.4^  \'2gH 
Ibs.  per  second.  Multiplying  the  weight  by  the  distance 
through  which  it  falls,  H,  we  have  62.4^ 


X   H  = 

ft. -Ibs.  of  work  per  second  and  $oo.6c)BH*  X  60 
ft. -Ibs.  per  minute.  Dividing  this  by  33,000,  we  have,  ap- 
proximately, the  horse-power  developed  by  the  stream  = 

500.69^77^  x  60  _ 

33,000 

This  is  usually  called  the  water  H.P. ,  because  it  is  the 
horse-power  which  the  stream  is  capable  of  producing  with  an 
ideal  water-motor,  that  is,  in  which  there  are  no  losses  such 
as  friction,  etc.  Fig.  234  shows  an  undershot  wheel  in  which 
the  water  passes  under  the  wheel. 

Fig-  235  shows  a  breast-wheel.  In  this  case  the  water 
strikes  the  wheel  at  or  near  the  level  of  the  axis.  These 
wheels  are  furnished  with  vanes  or  buckets  of  such  shape  that 


FIG.  234. — Undershot  Wheel.  FIG.  235. — Breast-wheel. 

not  only  will  they  admit  water  without  hindrance,    but  also 
return  it  to  the  lowest  possible  point  on  the  wheel.      The  flow 


3oo  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

of  water  is  controlled  by  large  gate-valves.  These  wheels 
require  comparatively  large  amounts  of  water  for  their  running, 
hence  their  efficiency  is  small.  For  the  plants  of  the  present 
time  the  wheel  would  necessarily  be  so  large  that  its  construc- 
tion and  operation  would  be  impracticable.  For  these  reasons 
they  have  largely  gone  out  of  use. 

TURBINES. 

In  a  parallel-flow  turbine  the  water  enters  and  leaves  the 
turbine  in  a  line  parallel  to  the  axis.  In  the  radial-flow  turbine 
the  water  enters  and  leaves  the  turbine  on  radial  lines,  flowing 
inward  or  outward  according  to  the  class  of  turbine.  In  a 
mixed-flow  turbine  the  water  enters  radially  and  leaves  in  a 
line  parallel  to  the  axis. 

The  outward-flow  turbine  included  in  the  classification  is 
shown  in  principle  in  Fig.  236.  In  the  centre  are  a  number 
of  fixed  curved  guides  which  direct  the  water  against  the 
curved  vanes  or  buckets  of  the  wheel,  causing  it  to  rotate  in 


FIG.  236.— Outward-flow  Turbine.       FIG.  237.— Inward-flow  Turbine. 

the  direction  shown  by  the  arrow.     The  action  of  the  water 
in  the  turbine  is  also  illustrated  by  the  arrows. 

Fig.  237  shows  the  principle  of  the  inward-flow  turbine.  In 
this  instance  the  water  enters  from  the  outside,  being  directed 
by  the  curved  guides  against  the  vanes  or  buckets  of  the 
wheel  and  leaves  at  the  interior.  The  curves  of  the  wheels 
and  the  guides  are  designed  such  that  a  maximum  efficiency 
may  be  obtained. 


WATER-POWER. 


3or 


The  larger  number  of  American  turbines  belong"  to  the 
mixed-flow  type. 

Fig.  238  shows  a  turbine  of  this  type.  The  water  flows 
from  the  outside  inward  through  the  openings  between  the 
guides,  strikes  the  wheel  or  runner  and  flows  out  through  the 


FIG.  238. 

bottom.  The  vanes  join  runners  at  the  bottom  by  means  of 
vertical  curves.  The  reaction  of  the  water  on  these  vanes 
causes  the  wheel  to  revolve. 


302  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


FIG.  239.— The  New  American  Turbine-wheel. 


FlG.  240. — Runner-case  and  Guides. 


WATER-POWER.  303 

Fig.  239  shows  the  runner  and  shaft  which  when  in  opera- 
tion are  vertical.  Fig.  240  shows  a  horizontal  section  of  the 
runner-case  and  guides.  C  is  a  guide,  B  is  a  vane  of  the 
runner,  usually  called  a  bucket,  and  A  is  a  gate.  The  i'nflow  of 
water  into  the  machine  is  controlled  by  these  gates.  The  open- 
ing between  the  guides  may  be  closed  by  means  of  the  gates, 
and  the  machine  stopped.  The  efficiency  of  a  water-turbine 
of  this  type  depends  largely  upon  the  curves  of  the  guides  or 
chutes  and  the  buckets.  By  giving  them  the  proper  curves 
the  least  resistance  and  greatest  working  effect  is  produced. 

Runner. — The  runner  of  this  turbine  is  a  solid  casting, 
though  in  some  makes  the  buckets  are  of  steel,  moulded  to  a 
cast  hub  and  rim.  The  very  high  speed  requires  that  it  be 
made  very  strong. 

Transmission. — The  power  developed  by  the  turbine  is 
transmitted  to  machinery  from  the  runner-shaft  by  suitable 
gearing. 

Manner  of  Applying  Water. — Fig.  238  shows  a  method 
used  for  conducting  water  to  and  from  the  wheel.  The  wheel 
is  placed  in  this  case  over  an  opening  in  the  "head-race" 
or  flume-floor  so  that  the  water  has  to  pass  through  the  tur- 
bine in  order  to  get  into  the  ' '  tail-race  ' '  which  is  below 
this  floor.  The  level  of  the  water  in  the  "tail-race,"  is  kept 
constant.  Sometimes  the  pipe  leading  to  the  tail-race,  called 
a  suction-tube,  is  made  very  long  in  order  to  produce  suction. 
The  limit  of  course  would  be  28  feet. 

Fig.  241  shows  a  turbine  located  in  an  iron  suction-tube 
about  20  feet  above  the  tail- water  level.  From  this  it  is 
readily  seen  that  the  turbine  is  entirely  in  water  while  in 
operation.  That  part  of  the  flume  A  above  the  turbine  is  the 
head-race,  that  part  in  which  the  wheel  is  contained  is  the  pit, 
and  that  part  below  the  turbine  is  the  tail-race.  C  is  the 
draft-  or  suction -tube. 

The  water  for  the  turbine  is  controlled  iit  its  passage 
through  the  'head-flume  by  means  of  large  gate- valves.  Fig. 
242  shows  one  operated  by  a  crank  and  gearing  or  by 


304 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


FIG.  241. — Suction-tube  (New  American  Turbine). 


WATER-POWER. 


3°5 


hydraulic  power.      By  means  of  this  valve  the  water  may  be 
shut  off  from  the  machine  for  examination,  repairs,  etc. 


FIG.  242. — Gate. 

Fig.  243  shows  the  arrangement  of  a  turbine  plant  (Victor). 
A  is  the  head-race  constructed  of  masonry.      B  is   the  head 


306 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


gate-valve.  C  is  the  head-flume.  D  is  the  shaft  to  which  the 
wheels  are  fastened  (the  turbines  are  not  seen,  being  covered 
by  the  iron  casing).  E  is  the  draft-tube,  and  .Fis  the  tail-race, 
constructed  also  of  masonry.  The  head  is  the  vertical  dis- 


FIG.  243. — Turbine  Plant. 

tance  from  the  water-level  in  the  tail-race  to  the  level  of  the 
supply-water. 

RATING    OF    TURBINES. 

Water-turbines  are  rated  according  to  the  horse-power 
they  will  develop. 

For  the  same  head  and  quantity  of  water  different  makes 
of  turbines  will  give  different  horse-power,  according  to  the 
excellence  of  design.  These  turbines  are  designed  for  plants 
in  which  a  large  quantity  of  water  is  at  hand,  but  with  com- 
paratively small  head.  Hence  the  quantity  of  water  is  a  factor 
which  affects  the  horse-power.  The  head  used  for  these  is 
usually  not  over  100  feet.  It  has  already  been  explained  how 
to  find  the  water  horse-power.  The  horse-power  which  the 


WATER-POWER.  307 

wheel   really   develops   will   always   be   less  than  this.      The 

wheel  H.P. 

efficiency  =  -  TT  p   ,  is  60  to  90  per  cent,   according  to 

\VcLLcr  irj. .  A  • 

make  of  wheel. 

The  wheel  horse-power  may  be  found  by  means  of  a 
dynamometer. 

SPEED    OF    TURBINE. 

The  velocity  of  the  wheel  is  due  to  the  velocity  of  the 
water.  Theoretically  the  velocity  of  the  wheel  would  be  the 
velocity  of  the  water,  but  actually  this  is  not  the  case.  A  tur- 
bine attains  its  greatest  efficiency  when  the  velocity  of  the 
turbine  is  one  half  that  of  the  water  driving  it.  The  actual 
speed  can  be  gotten  by  a  test  with  a  speed-indicator. 

REGULATION. 

The  speed  of  the  turbine  is  regulated  by  closing  the  water- 
supply  to  the  turbines  by  some  automatic  or  hand-apparatus. 
Fig.  244  shows  the  Snow  centrifugal  governor  for  water-tur- 
bines. It  has  a  foundation  of  its  own  and  is  connected  to  the 
turbine-shaft  by  means  of  a  belt  to  the  pulley  A .  R  is  the 
shaft  which  operates  the  valve  which  closes  the  water-supply. 
If  the  turbine  is  running  at  normal  speed  the  shaft  R  is  not 
revolved  by  the  governor.  If  the  speed  is  increased,  however, 
above  the  normal  the  balls  rise  and  the  governor-spindle  is 
lowered  thereby  causing  S  and  R  to  revolve  in  such  a  direction 
as  to  close  the  gates. 

If  the  speed  is  decreased  below  the  normal  the  governor- 
balls  descend  and  operate  a  mechanism  which  turns  S  and  R 
in  such  a  direction  as  to  open  the  sluice-gates.  By  means  of 
a  hand- wheel  the  shaft  R  may  be  operated  by  hand. 

SETTING. 

The  head-race  should  be  made  sufficiently  large  to  prevent 
a  diminution  of  the  head  by  friction,  etc.  It  is  usual  to  make 
the  head-race  of  such  cross-section  that  the  water  will  not  flow 
through  it  faster  than  100  feet  per  minute. 


3c8 


PUMPS,  GAS  ENGINES,  WATER-POWER,  ETC. 


Making  the  head-race  too  small  is  equivalent  to  reducing 
the  head. 

The  wheel-pit,  that  is,  where  there  is  no  draft-tube,  should 
be  of  sufficient  depth  that  it  will  not  produce  a  reaction  of  the 
water  against  the  under  side  of  the  wheel. 


FIG.  244. — Snow  Centrifugal  Governor. 

An  additional  loss  of  power  is  also  caused  by  the  fact  that 
a  portion  of  the  head  is  consumed  by  forcing  the  water  out  of 
the  pit  when  the  outlet  is  of  insufficient  size.  The  pit  should 
be  lined  so  that  its  bottom  and  sides  will  not  be  damaged  by 
erosion. 

The  tail-race  should  also  be  both  wide  and  deep. 


WA  TER-POWER.  309 

The  flume  should  be  large  also,  in  fact,  all  the  water- 
passages  should  be  large  enough  to  prevent  loss  of  head  on 
account  of  friction, 

DRAFT-TUBES. 

This  is  an  air-tight  tube  used  in  constructions  where  the 
wheel-pit  is  very  deep.  Its  lower  end  should  dip  2  or  3  inches 
below  the  surface  of  tlie  standing  tail-water.  It  is  never  longer 
than  28  or  30  feet,  and  is  usually  less.  It  is  sometimes  very 
short,  say  2  to  3  feet,  simply  for  the  purpose  of  carrying  the 
water  so  that  it  is  out  of  reach  of  the  lower  timbers  of  the 
penstock. 

IMPULSE-    OR   JET- WHEELS. 

This  class  consists  of  those  water-motors  utilizing  small 
volumes  of  water  with  high  heads  by  the  use  of  a  jet  escaping 
from  a  nozzle  and  striking  against  buckets  which  are  placed 
upon  the  circumference  of  a  wheel,  thus  producing  motion. 

An  example  of  this  type  is  found  in  the  Pelton  motor- 
wheel,  Fig.  245,  mounted  upon  a  wood  frame.  The  water- 
supply  issues  in  a  jet  from  the  nozzle  and  strikes  the  buckets 
of  the  wheel. 

The  supply  is  controlled  by  a  valve. 

The  speed  is  kept  constant  under  varying  loads  by  means 
of  a  centrifugal  governor  which  closes  or  opens  the  supply 
according  to  the  needs  of  the  load.  The  action  of  this 
governor  is  the  same  in  effect  as  that  described  for  the  turbine. 
The  discharge  or  tail-water  leaves  the  motor  at  the  bottom. 
Fig.  246  shows  this  wheel  mounted  in  an  iron  case,  which 
arrangement  makes  the  setting  of  the  motor  a  more  convenient 
matter. 

A  Pelton  motor-wheel  is  shown  also  in  Fig.  254,  driv- 
ing an  air-compressor.  With  a  low  head  and  large  volume 
of  water  the  arrangement  shown  in  Fig.  247  is  used,  in 
which  three  nozzles  direct  as  many  jets  against  the  same 
wheel. 


310  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC, 

~"   . 


WATER-POWER.  311 

The  motors  require  practically  the  same  setting  as  tur- 
bines. 

The  horse-power  of  these  wheels  may  be  determined  by 
means  of  a  dynamometer. 

wheel  H.P.  . 
The  efficiency  =  —  is  comparatively  high. 

The  simplicity  of  this  arrangement  makes  it  very  desirable. 


FIG.  246.—  Pelton  Water-motor. 


HYDRAULIC    PUMP. 


It  has  been  stated  already  that  steam-engines  with  slight 
modifications  may  be  used  as  water-engines,  in  which  case 
water  is  used  as  the  working  fluid  instead  of  steam. 

Reciprocating  water-engines  are  necessarily  of  slow  speed 


3*2 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


because  of  the  incompressibility  of  water  and  its  large  amount 
of  friction  in  passing  through  pipes  as  compared  with  steam. 

Fig.    248    shows   a   pump  driven   by  water-pressure.      Its 
construction  does  not  differ  materially  from  that  of  the  steam- 


FIG.  247. — Multiple  Jet-wheel. 

pump  except  that  the  driving  cylinders  are  provided  with  extra 
large  passages  suitable  for  the  prompt  and  easy  flow  of  water. 
Loss  of  Head. — In  any  water-engine  the  pressure  upon  the 
piston  or  buckets  is  theoretically  found  by  the  formula  already 

pS 
given,  H  =  — .     However,  it  is  found  that  part  of  this  pressure 


WATER-POWER. 


3*3 


314  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

is  lost  in  overcoming  friction  on  its  way  through  pipes,  etc. 
This  loss  is  called  "loss  of  head,"  since  it  is  equivalent  to 
diminishing  the  height  of  the  supply  above  the  motor.  This 

4/v* 

loss  of  head  for  a  straight  pipe  is  h  —  f-j — ,  in  which  /  =  length 

<5 

and  d  =  diameter  of  the  tube,  both  in  feet,  v  =  velocity  in 
feet  per  second  and  f  —  a  coefficient  which  Weisbach  gives 

.01288/z/2 
to  be  .00644,  which  makes  h  =  -  —-, . 

This  loss  must  be  subtracted  from  the  measured  head  when 
designing  a  motor  to  do  given  work. 

Flow  of  Water  Through  Orifices. — The  theoretical  velocity 
of  water  flowing  from  an  orifice  is  V  2gH,  or  that  of  a  falling 
body,  but  the  actual  velocity  is  less  than  this. 

The  actual  velocity  at  the  plane  of  the  orifice  is  generally 
about  .97  of  that  due  to  head,  that  is,  .97  \/2gH. 

The  discharge  then  would  be  Q  =  Av,  where  A  —  area 
of  the  orifice  in  Fig.  249. 


FIG.  249. 

The  jet  contracts  on  leaving  the  orifice  as  shown  at  N. 
This  contracted  area  is  called  the  "  Vena  Contracta. " 
In  calculating  the  discharge  the  velocity  is  multiplied  by 
the  area  of  the  cross-section  of  the  jet  at  this  point  instead  of 
the  area  of  the  orifice.      This  area  is  usually  about  .64  of  the 
area  of  the  orifice.      Hence  multiplying  the  velocity  .97  V 2gH 
by     the     area     .64 A,    we     have     Q  —  .64 A   X   -97  V2gH  = 
.62A  ^2gH  as    the    discharge   volume.       By    means    of  this 
formula  the  size  of  pipe,  head,  and  velocity  may  be  compared. 


WATER-POWER. 


315 


Tables,  however,  are  given  by  authorities  which  take  in  con- 
sideration more  minutely  the  difference  of  flow  due  to  the 
smoothness  or  roughness  of  pipes,  whether  larger  or  smaller, 
etc.,  to  which  the  author  refers  the  student. 

MEASURING   THE    POWER    OF    STREAMS. 

The  principal  method  used  is  that  of  obtaining  the  velocity 
of  the  stream,  as  a  creek  or  river,  and  then  multiplying  it  by 
the  area  of  the  cross-section  of  the  stream. 

Let  Q  —  Av,  in  which  Q  is  the  discharge  in  cubic  feet  per 
minute  and  A  the  area  of  the  cross-section  in  square  feet,  and 
i'  the  velocity  in  feet  per  minute. 

A  may  be  found  approximately  by  taking  the  depth  at 
regular  intervals  across  the  stream,  the  distance  from  the  edge 
to  the  first  sounding  being  one  half  that  of  the  other  intervals. 

By  adding  these  different  depths  and  dividing  by  the 
number  of  soundings  the  mean  or  average  depth  is  obtained. 
Multiply  this  average  depth  by  the  width  at  the  surface  and 
the  result  is  approximately  the  area  of  the  cross-section  of  the 
stream. 

7'  is  found  in  different  ways. 

A  simple  method  sometimes  used  is  that  in  which  a  float 
is  placed  on  the  stream  and  the  time 
it  requires  to  pass  over  a  known  dis- 
tance noted. 

The  velocity  of  the  float  will  be 
that  of  the  water  at  the  surface    of 
the   stream,   the  velocity  being  less 
toward  the  bottom  than  at  the  top. 
The  mean  or  average  velocity  is  gen-        _H 
erally  taken  in  practice  as  about  .  80 
of  the  surface  velocity. 

Another  simple  method  of  finding 

the  surface  velocity  is  by  means  of  a  > 

Pitot  tube.   This  is  shown  in  Fig.  250.        FlG-  25o--Pitot  Tube. 

The  velocity  of  the  water  passing  the  opening  at  C  causes 


3^6  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

the  water  to  rise  in  the  tube  to  a  height  varying  with  the 
velocity  of  the  water.  Let  //  be  the  height  of  the  column  of 
water  in  the  tube.  The  velocity  is  theoretically  v  =  \f2gk. 

For  small  streams  the  quantity  of  water  which  the  stream  is 
capable  of  supplying  is  determined  as  shown  in  Fig.  251. 


FIG.  251. — Weir. 


This  method  is  called  the  "Weir-dam  Measurement" 
and  is  more  exact  than  the  method  just  shown. 

A  notch  is  cut  in  a  thick  plank,  the  length  of  the  notch 
being  about  two  thirds  the  width  of  the  stream.  Stakes  are 
driven  in  the  ground  and  this  plank  is  held  by  them  so  that 
the  water  of  the  stream  passes  through  the  notch.  To  find 
the  depth  of  the  stream  flowing  through  the  notch,  proceed  as 
follows : 


WATER-POWER.  3!7 

In  the  stream  about  6  feet  above  the  dam  drive  a  stake  in 
the  channel  and  mark  a  point  on  it  level  with  the  bottom  of 
the  notch.  Then  when  the  water  is  all  flowing  over  the  dam, 
mark  the  water-level  on  the  stake.  The  distance  between 
these  two  marks  is  the  depth  of  the  stream.  Then  find  the 
width  of  the  notch  in  feet,  which  gives  the  cross-section  of  the 
stream.  The  quantity  of  water  flowing  in  the  stream  is  then 
determined  by  the  following  formulae,  given  by  Francis: 


if  the  notch  is  taken  the  full  width  of  the  stream; 


if  the  notch  begins  at  one  edge  of  the  stream  and  does  not 
extend  completely  across  ; 


if  the  notch  is  in  the  middle  of  the  stream,  and  does  not  reach 
either  edge. 

In  each  case  Q  —  quantity  of  water  flowing  in  cubic  feet 
per  second  ;  /  =  length  of  weir-notch  in  feet  ;  //  =  head  of 
water  on  the  crest  in  feet,  measured  as  shown  above. 

PROBLEMS. 

1.  The   power  of  a  certain  stream  is  utilized  by  a  Pelton  water- 
wheel  TOO  feet  below  the  source.      Find  the  pressure  per  square  inch 
due  to  the  head;  also  the  pressure  per  square  foot. 

2.  Find  the  velocity  of  the  jet  which  strikes  the  buckets  in  feet 
per  second,  neglecting  friction,  in  the  above. 

3.  Find  the  actual  volume  of  water  in   cubic  feet   discharged  per 
hour  by  a  head  of  150  feet  through  a  pipe,  the  nozzle  of  which  is  4 
inches  in  diameter,  taking  the  friction  into  account. 

4.  A  stream  is  20  feet  wide  and  12  inches  deep.      Its  mean  veloc- 
ity is  400  feet  per  minute.      Find  the  horse-power  it  is  capable  of  pro- 
ducing. 

5.  A  certain  water-turbine  uses  4536  cubic  feet  of  water  per  min- 
ute with  a  head   of  50  feet.      Its   developed  horse-power  is   342  as 
measured  by  a  dynamometer.      Find  the  efficiency. 


3i8  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

6.  A  pipe  12  inches  in  diameter  and  600  feet  long  supplies  water 
to  a  water-wheel.      Find  the  loss  of  head  in  feet  due  to  friction,  by 
Weisbach's  formula. 

7.  If  the   difference   in   level   of  the  two  ends  of  the  pipe  in  the 
above  is  500  feet,  find  the  effective  head. 

8.  Suppose  that  the  water  rises  to  a  height  of  6  inches  in  a  Pitot 
tube  due  to  the  velocity  of  the  water.     Find  the  velocity  of  the  water. 

9.  The   dimensions  of  a  weir  are  7—42  inches;   the  weir  is  in 
the  middle   of  the   stream.     The   depth  of  water  on   the  weir  is  16 
inches.      Find  the  quantity  of  water  flowing  in  the  stream. 

10.  Suppose  that  in  problem  9  the  weir  was  the  full  width  of  the 
stream,  72  inches.     Find  h  in  this  case. 


CHAPTER    XXVI. 
COMPRESSED   AIR. 

COMPRESSED  air  is  used  principally  as  a  means  of  trans- 
mitting power  through  moderately  long  distances.  In  a 
common  steam-plant  considerable  steam  is  condensed  in  the 
pipes  before  it  reaches  the  motor.  The  greater  the  distance 
the  greater  will  be  these  losses.  For  very  great  distances  the 
use  of  steam  for  power  transmission  becomes  impracticable,  and 
either  electric  transmission  or  compressed-air  transmission 
must  be  used. 

The  power  of  a  waterfall  or  that  of  a  steam-engine  may  be 
used  for  compressing  air  up  to  a  high  pressure,  and  this  air  is 
then  conducted  through  pipes  to  the  air-motor — which  may  be 
similar  to  a  common  steam-engine — or  may  have  other  forms, 
according  to  the  kind  of  work  to  be  done.  Since  the  air  after 
losing  the  heat  given  to  it  by  compression  is  not  subject  to 
condensation  by  thfc  atmosphere  as  in  the  case  of  steam,  the 
air  may  be  transmitted  through  many  miles  of  piping  without 
any  other  loss  except  that  due  to  friction  and  possible  leakage. 
Another  example  of  the  use  of  compressed  air  is  that  of  mining 
operations.  The  power-plant  of  the  mine  must  be  above 
ground.  Underground  there  are  a  great  number  of  rock- 
drills  and  locomotives  for  hauling  ore  through  the  mine,  which 
must  be  operated  by  some  means.  Steam  is  objectionable 
because  it  will  have  to  be  exhausted  into  the  interior  of  the 
mine,  producing  damp,  etc.  Besides  this  the  loss  due  to  con- 
densation would  be  large  because  of  the  distance  between  the 
boiler  and  the  motor.  By  means  of  steam  or  other  power  air 


320  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

may  be  compressed  at  the  entrance  to  the  mine  and  conducted 
through  pipes  with  small  losses  to  the  motors.  The  exhaust 
into  the  mine  starts  a  current  of  air  towards  the  mine-entrance, 
thus  tending  to  rid  the  mine  of  poisonous  or  objectionable 
gases. 

MANNER    OF   COMPRESSING    AIR. 

Air  is  taken  from  the  atmosphere  and  given  a  high  pressure 
by  means  of  an  air-compressor. 

Air-compressors  may  be  classified  according  to  the  manner 
in  which  the  air-pistons  are  given  their  motion,  as  steam- 
driven,  belt-driven,  and  water-driven.  Compressors  are  also 
classified  according  to  the  number  of  air-pistons,  as  single- 
stage  compressors  and  double-stage,  or  compound,  com- 
pressors, corresponding  to  the  simple  and  compound  steam- 
engine. 

The  steam-driven  compressor  consists  of  an  ordinary 
steam-engine  usually  having  the  air-  and  steam-pistons  fastened 
to  the  same  piston-rod.  Double-stage  compressors  may  be 
either  tandem  or  cross-compound,  similar  respectively  to 
tandem  and  cross-compound  steam-engines. 

In  belt-  or  gear-driven  compressors  the  driving  power  may 
be  taken  from  a  shaft,  instead  of  being  actuated  directly  by 
steam-  or  water-power.  The  shaft  of  the  compressor  carries  a 
large  pulley  or  gear-wheel,  taking  power  from  the  motor-shaft 
by  means  of  a  belt  or  gear-wheels. 

The  water-impulse  compressor  is  shown  in  Fig.  254. 
The  impulse-wheel  is  mounted  directly  upon  the  main  shaft  of 
the  machine.  The  wheel  is  put  in  motion  by  turning  on  a  jet 
of  water  from  the  pipe  at  the  bottom.  The  force  of  the  water 
against  the  buckets  produces  rotary  motion.  The  force  of  the 
jet  is  controlled  by  means  of  the  hand-valve  at  the  left  of  the 
cut. 

The  process  of  compression  in  a  double-stage  compressor 
takes  place  as  follows:  The  air  is  drawn  into  the  low-pressure 
or  intake  cylinder  and  is  partially  compressed,  after  which  it 


PUMPS,  GAS  ENGINES,  WATER-POWER,  ETC. 


COMPRESSED  AIR. 


323 


324  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

passes  through  an  intercooler,  where  the  heat  of  compression 
is  taken  away  by  means  of  cold  water.  It  is  then  drawn  into 
the  high-pressure  cylinder,  where  it  is  compressed  to  a  higher 
pressure,  and  then  it  passes  to  an  air-receiver  and  thence 
through  the  pipe-line  to  the  motors. 

Details  of  Compressors. — The  general  arrangement  of  the 
parts  of  an  air-compressor,  is  similar  to  that  of  a  steam-engine 
with  a  few  exceptions,  which  will  be  explained. 

Cylinders  and  Valve-chest. — The  valves  and  steam-chest 
are  the  same  as  for  a  steam-engine.  Usually,  the  Corliss  valve 
is  used,  though  some  manufacturers  use  poppet-valves  for 
admitting  the  air.  Fig.  252  shows  the  Corliss  valve  used  in 
the  intake  air-cylinder  of  the  Norwalk  Compressor  and  poppet- 
valves  in  the  high-pressure  air-cylinder.  The  higher  pressure 
in  this  cylinder  makes  it  possible  to  use  the  poppet-valve  more 
successfully  without  chattering,  whereas  in  the  low-pressure 
cylinder  the  low  pressure  and  the  spring  would  cause  a  con- 
stant vibration  of  the  valve  against  its  seat,  thus  producing  an 
objectionable  noise.  When  air  is  compressed  its  temperature 
rapidly  increases.  In  order  to  keep  the  temperature  of  the 
cylinder-walls  from  being  unduly  heated,  the  air-cylinders  are 
usually  surrounded  with  a  space  through  which  water  is  circu- 
lated. The  following  table  shows  the  theoretical  increase  of 
temperature  of  compression  without  jacketing: 

Temperature  of  air  before  compression,         60°        90° 
"  "    compressed  to  15  Ibs.   177°      212° 

30    "      255°      294° 

60    "      369°     417° 

-  90   "     455°     507° 

.     •"  120    "       524°       580° 

Formerly  the  temperature  due  to  compression  was  lowered 
foy  means  of  an  injection  of  cool  water,  but  its  use  has  been 
discontinued  for  the  following  reasons: 

ist.  The  presence  of  water  on  the  inside  of  the  cylinder 
may  make  it  unsafe  to  run  the  compressor  at  speeds  which 
would  otherwise  be  safe  and  proper. 


\COMPRESSED  AIR.  325 

2ci.  With  the  use  of  water  in  the  compression-cylinder  it 
would  be  impossible  to  lubricate  the  surface  of  the  cylinder. 
With  water  in  the  cylinder  and  the  dirt  and  grit  which  usually 
accompanies  it,  the  piston  and  cylinder  surface  wear  more 
rapidly. 

THE    INTERCOOLER. 

The  intercooler  is  used  only  on  compressors  which  have  at 
least  two  stages  of  compression.  It  consists  of  a  large  chamber 
E,  Fig.  252,  situated  between  the  low-pressue  and  high-pressure 
cylinders,  which  has  small  pipes  in  it  through  which  cool  water 
circulates.  As  already  stated,  the  low-pressure  piston  com- 
presses the  air  and  raises  its  temperature.  The  object  of  the 
intercooler  is  to  reduce  the  air-temperature  before  it  enters  the 
high-pressure  cylinder.  This  reduces  the  power  required  to 
finish  the  compression,  because  the  reduction  of  the  temperature 
reduces  the  pressure  and  thereby  lessens  the  power  of  steam 
required  to  run  the  compressor.  Imagine  a  cylinder  of  any 
capacity,  say  2  cubic  feet,  containing  air  at  a  temperature  of 
say  369°  at  a  pressure  of  60  Ibs.  per  square  inch.  Then  if  by 
any  means  we  can  cool  the  temperature  down  from  369°  to 
255°,  the  pressure  is  reduced  from  60  Ibs.  to  30  Ibs.,  accord- 
ing to  the  table.  Then  the  air  at  30  Ibs.  pressure  can  be 
further  compressed  with  less  power  than  air  at  60  Ibs. 

The  heat  produced  by  compression  will  be  dissipated  sooner 
or  later;  if  not  in  the  compressor,  then  in  the  pipe  after  it  leaves 
the  compressor,  so  that  the  final  pressure  will  be  approximately 
the  same  whether  the  cooling  is  in  the  compressor  itself  or 
after  it  leaves  it. 

Ratio  of  Volume  of  Air-cylinders. — The  ratio  of  the 
volume  of  the  low-pressure  air-cylinder  to  that  of  the  high- 
pressure  cylinder  will  be:  R  —  ,,;  where  A'  is  the  ratio  and  D 

and  ^the  diameters  of  low-  and  high-pressure  pistons.    R  differs 

with  different  sizes  and  makes,  but  is  usually  taken  from  2  to  3. 

Fly-wheel. — By    taking     indicator-cards     from    both    the 

steam-  and  air-cylinders  of  a  compressor  it  will  be  found  that 


326 


PUMPS,  GAS-ENGINES,   WATER-POWER,  ETC. 


at  the  beginning  of  a  stroke  the  pressure  in  the  steam-cylinder 
is  at  a  maximum  (practically  boiler-pressure)  and  the  pressure 
in  the  intake  air-cylinder  is  at  a  minimum.  This  evidently 
tends  to  make  a  very  unbalanced  state  of  running,  the  effect 
being  to  run  fast  at  the  beginning  of  the  stroke,  with  a  gradual 
slowing  up  toward  the  end  of  the  stroke.  In  order  to  balance 
the  compressor  and  partly  counteract  this  effect  the  fly-wheels 
are  usually  made  very  heavy,  and  in  fact  the  whole  compressor 
is  made  massive  in  order  to  withstand  the  fluctuating  strains. 

The  Air-receiver. — The  air-receiver  is  not  a  part  of  the 
compressor  itself,  but  it  is  a  necessity  in  any  compressed-air 
system.  It  is  a  large  tank  into  which  the  air  passes  after  leav- 


FIG.  255. — Air  receiver. 

ing  the  compressor.  It  corrects  the  pulsating  effect  caused 
by  the  periodic  expulsions  of  the  air  from  the  compressor  into 
the  line  of  piping.  If  the  distance  from  the  compressor  to  the 
motor  is  great  it  is  best  to  use  two  air-receivers,  one  near  the 
compressor  and  one  near  the  motor.  The  first  receiver  is  pref-, 
erably  placed  far  enough  away  from  the  compressor  so  that  a 
great  part  of  the  heat  of  compression  may  pass  off  to  the 
atmosphere  through  the  pipe  before  the  receiver  is  reached. 


COMPRESSED  AIR.  327 

Usually  about  50  feet  is  sufficient.  Fig.  255  shows  a  receiver 
made  by  the  Rand  Drill  Company.  Another  use  of  the  receiver 
is  to  catch  any  moisture  in  the  air  that  may  be  condensed 
by  the  cooling  and  allow  it  to  be  drawn  off  from  the  bottom  of 
the  receiver.  Additional  moisture  may  be  deposited  in  the 
pipe-line  and  carried  to  the  second  receiver,  where  it  may  be 
drawn  off  before  reaching  the  motor. 

Regulation. — Compressors  are  usually  governed  by  a  bail- 
or throttling-governor  which  works  in  combination  with  an 
automatic  regulator  so  that  the  steam  is  throttled  more  or  less 
according  to  the  air-pressure,  so  that  the  machine  runs  just  fast 
enough  to  supply  the  demand  for  air.  In  this  way  no  more 
air  is  compressed  than  is  used,  thus  economizing  the  power. 
Fig.  256  shows  the  regulating 
arrangement  used  on  the  Rand 
compressor.  It  consists  of  an 
ordinary  ball-governor  placed  on 
the  steam-pipe  with  the  addition 
of  a  small  air-cylinder  which  has 
a  pipe-connection  with  the  exit- 
pipe  of  the  compressor.  When 
the  pressure  of  air  becomes  ex- 
cessive the  piston  of  the  air- 

I   .        .  ,      ,  ,   .,  .  FIG.  256. 

regulator  is  pushed  up  and  this 

in  turn  closes  the  governor-valve  and  diminishes  the  speed  of 
the  compressor.  If  the  air-pressure  becomes  low  the  large 
ball  at  the  right  of  the  figure  causes  the  governor-valve  to  open 
and  the  speed  of  the  compressor  to  be  increased. 

MOTORS. 

Compressed  air  may  be  substituted  for  steam  in  almost  any 
of  its  uses  and  it  can  be  used  in  any  steam-driven  motor,  since 
the  laws  of  expansion  of  steam  and  air  are  practically  the  same. 
Compressed  air  has  the  advantage  of  being  more  easy  of  trans- 
portation than  steam  for  the  reason  stated  before,  that  is,  it  can 
be  taken  through  long  distances  in  pipes  without  condensation 


328  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

losses.  One  of  the  most  important  uses  of  compressed  air 
is  in  mining  operations,  the  rock-drills  being  operated  by 
compressed  air.  Fig.  257  shows  the  details  in  section  of  the 
actuating  mechanism  of  a  rock-drill,  manufactured  by  the 
Rand  Drill  Company.  The  valve  is  a  plain  slide-valve,  always 
thrown  in  the  same  direction  in  which  the  piston  is  moving, 


FIG.  257.  — Rock-drill. 

and  is  operated  by  a  three-arm  rocker  which  is  held  in  place 
by  a  pin.  This  rocker  is  placed  in  a  recess  of  the  cylinder 
between  the  ends  of  the  double-headed  piston,  a  part  of  which 
is  in  section,  and  its  upper  arm  engages  the  valve.  As  the 
piston  reciprocates  it  moves  the  rocker  and  valve  in  the  direc- 
tion in  which  it  is  going. 

Another  important  use  of  compressed  air  is  found  in  the 
present  system  of  braking  trains.  In  this  system  a  steam- 
driven  compressor,  called  the  air-pump,  which  compresses  a 
constant  air-supply  into  a  main  reservoir,  is  mounted  on  the 
locomotive.  From  this  reservoir  the  air  is  taken  to  auxiliary 
reservoirs,  one  under  each  car,  by  means  of  the  train-pipe. 
The  air  is  kept  at  a  uniform  pressure  of  70  pounds  per  square 
inch,  by  means  of  a  governor  on  the  pump,  in  both  the  train- 
pipe  and  reservoirs.  When  it  is  desired  to  apply  the  brakes, 
the  engineer  by  means  of  the  engineer's  valve  in  the  cab 
reduces  the  pressure  in  the  train-pipe.  This  actuates  a  valve, 
called  the  triple-valve,  placed  under  each  car.  The  triple- 
valve  on  opening  allows  air  to  pass  into  the  brake-cylinder 
under  the  cars;  it  moves  a  piston,  which  is  connected  to  the 
brake-shoes  by  a  series  of  levers.  The  brakes  are  released 
by  restoring  the  pressure  in  the  train-pipe;  this  causes  the 


COMPRESSED  AIR.  329 

triple-valve  to  open  a  passage  to  the  atmosphere;  from  the 
brake-cylinder,  thus  allowing  the  air  to  escape.  A  spring 
returns  the  piston  to  its  original  position.  For  an  emergency 
stop,  the  pressure  in  the  train-pipe  is  reduced  suddenly,  and 
the  triple-valve  opens  in  such  a  manner  as  to  allow  air  from 
both  the  train-pipe  and  the  auxiliary  reservoir  to  enter  the 
brake-cylinder,  thus  applying  the  brakes  with  full  force. 

Compressed  air  is  used  for  many  purposes  in  railroad  shops 
with  as  many  different  means  of  application,  of  which  limited 
space  forbids  a  description  here. 

LAWS    OF    AIR-PRESSURE. 

Air-pressures  in  a  compressed-air  system  are  measured  by 
a  common  pressure-gauge,  similar  to  a  steam-gauge.  For 
convenience  the  dial  sometimes  is  made  to  read  atmospheres 
instead  of  pounds.  A_n  atmosphere  corresponds  to  14.7  Ibs. 
per  square  inch.  The  pressure-gauge  ordinarily  indicates 
pressures  above  the  atmosphere. 

The  Absolute  Pressure  is  the  pressure  abo/e  a  perfect 
vacuum,  or  the  gauge-pressure  plus  14.7  Ibs. 

Free  Air. — This  is  the  term  commonly  used  for  air  at  the 
atmospheric  pressure;  that  is,  of  the  air  which  enters  the  intake- 
cylinder.  The  temperature  is  usually  measured  by  the  Fahren- 
heit scale.  Absolute  temperature  is  the  temperature  as 
indicated  by  the  thermometer  plus  461°  F.  Thus  at  the 
temperature  90°  by  the  thermometer,  the  absolute  temperature 
is  90°  -f-  461°  =  55  i°.  Likewise  for  temperatures  below  zero, 
a  temperature  of  —  20°  by  the  thermometer  would  give  —  20° 
-(-461°  =  441°  as  the  absolute  temperature. 

The  relations  of  volume,  pressure,  and  temperature  of  air 
may  be  given  as  follows: 

1.  The    volume    of  air   varies   inversely   as    the    absolute 
pressure  when  the  temperature  is  constant. 

2.  The   absolute   pressure   varies  directly  as  the   absolute 
temperature  when  the  volume  is  constant. 


330 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


3.  The  volume  varies   as  the  absolute  temperature  when 
the  pressure  is  constant. 

4.  The  product  of  the  absolute  pressure  and  the  volume  is 
proportional  to  the  absolute  temperature. 

These  laws  may  be  more  concisely  expressed  by  means  of 
the  equation: 

PV      P'V 


f         T' 

in  which  P,   V    T  are  the  pressure,  volume,  and  temperature 
respectively. 

The  following  table  shows  the  weight  and  volume  of  air  at 
different  temperatures. 

VOLUME,    DENSITY,    AND    PRESSURE    OF    AIR    AT     VARIOUS 
TEMPERATURES.     (D.   K.  CLARK.) 


Tempera- 
ture. 

Volume  of  One  Pound 
of  Air  at  Constant 
Atmospheric  Pressure. 
Volume  at  62°  F.  =  i. 

Weight  of 
i  Cu.  Ft. 
in  Pounds. 

Pressure  of  a  Given 
Weight  of  Air  and 
Constant  Volume. 
Atmospheric  Pressure 
at  62°  F.  =  i. 

Fahrenheit. 

Cubic  Feet. 

Pounds. 

Lbs.  per  Square  Inch. 

O° 

H.583 

.0863 

12.96 

32 

12.387 

.0807 

13.86 

40 

12.586 

.0794 

14.08 

50 

12.840 

.0778 

14.36 

62 

13.141 

.0760 

14.70 

90 

13.845 

.0722 

15-49 

140 

15.100 

.0662 

16.89 

2OO 

16.606 

.0602 

18.58 

25O 

17-865 

•0559 

19.98 

300 

19.  121 

.0522 

21.39 

4OO 

21.634 

.0462 

24.20 

500 

24.146 

.0414 

27.01 

600 

26.659 

•0375 

29.82 

Referring  again  to  the  relations  of  pressure,  volume,  and 
temperature  as  shown  in  i,  2,  3,  and  4,  a  diagram,  Fig.  258,  is 
produced  which  will  show  at  a  glance  conditions  as  deduced 
from  these  laws. 

The  figures  at  the  left  indicate    pressures  in  atmospheres 


COMPRESSED  AIR. 


331 


above  vacuum,  that  is,  absolute  pressures.     The  corresponding 
figures  at  the  right  denote  pressures  by  the  gauge  in  pounds. 


TEMPERATURE  FAHRENHEIT 
FIG.  258.* 


At  the  top  are  volumes  from  one  tenth  to  one.  At  the  bottom, 
degrees  of  temperature  to  1000°  Fahrenheit.  The  two  curves 
which  begin  at  the  lower  left-hand  corner  and  extend  to  the 

*  From  "  Compressed  Air." 


332  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

upper  right  are  the  lines  of  compression.  The  upper  one  is 
the  "  Adiabatic  "  curve,  that  which  represents  the  pressure  at 
any  point  on  the  stroke,  with  the  heat  developed  by  compres- 
sion remaining  in  the  compressed  air;  the  lower  is  the 
"  Isothermal,"  the  pressure  curve  when  the  heat  of  compres- 
sion is  abstracted  as  fast  as  compression  takes  place.  The 
three  curves  which  begin  at  the  lower  right-hand  corner  and 
rise  to  the  left  are  heat  curves,  and  represent  the  increase  of 
temperature  corresponding  to  different  pressures  and  volumes, 
assuming  in  one  case  that  the  temperature  of  the  air  before 
admission  to  the  compressor  is  zero,  in  snother  60°,  and  in 
another  100°.  We  see  by  referring  to  the  adiabatic  curve  that 
for  a  volume  of  one  cubic  foot  the  pressure  is  I  atmosphere. 
Again  for  a  volume  of  .5  cubic  feet  the  pressure  is  nearly 
3  atmospheres  absolute,  or  say  about  28  Ibs.  by  the  gauge; 
and  likewise  the  relation  of  pressure  to  volume  up  to  I  cubic 
foot  are  found. 

If  we  compare  the  compression  line  from  zero  with  the 
compression  line  from  100°  it  will  be  noticed  that  in  compress- 
ing the  air  from,  say  I  atmosphere  to  10  atmospheres,  the 
original  difference,  which  at  the  start  was  only  100°,  has  now 
become  about  200°,  and  for  a  pressure  of  20  atmospheres 
about  250°.  This  shows  that  it  is  highly  important  to  supply 
air  to  the  compression  as  cold  as  possible.  The  greater  the 
temperature  of  entering  air  the  greater  the  rise  in  temperature 
for  equal  amounts  of  compression.  Neither  the  adiabatic  or 
the  isothermal  curves  represent  the  exact  condition  of  the  air, 
but  where  there  is  a  system  of  cooling  the  air  during  compres- 
sion, the  lines  on  the  indicator-card  may  be  traced  between 
the  adiabatic  and  isothermal  lines.  For  purposes  of  calcula- 
tion, however,  the  adiabatic  may  be  used,  as  it  is  the  curve 
most  nearly  approached  in  practice. 

Intake-air. — As  already  stated,  the  air  used  for  compres- 
sion should  be  as  cool  as  possible  in  order  to  admit  of  the  best 
economy.  For  this  reason  it  is  not  considered  best  to  use  air 
direct  from  the  engine-room,  as  it  is  more  or  less  heated,  but 


COMPRESSED  AIR.  333 

it  should  be  taken  from  outside.  The  air  should  also  be  free 
from  dust,  for  which  reason  the  outer  end  of  the  conduit-pipe 
should  not  be  too  close  to  the  ground. 

Volume, and  Weight  of  Air  per  Minute. — The  quantity  of 
air  required  for  a  compressor  depends  upon  the  volume  of  the 
low-pressure  cylinder  and  the  velocity  of  the  piston. 


FIG.   259.  —  Indicator-card  taken  from  the  Steam-cylinder  of  a  Compressor. 

Knowing  the  length  of  the  stroke  in  feet,  Z,  and  the  area 

of  the   low-pressure  piston  in  square  inches,  A,  we  have  - 

144 

as  the  volume  in  cubic  feet  swept  over  by  the  piston  at  one 
stroke.  Multiplying  this  by  N,  the  number  of  strokes  per 

minute,  we  have  -    —  as  the  volume  in  cubic  feet  per  minute 
144 

passed  over  by  the  piston.  This  would  represent  the  total 
volume  of  air  used  if  there  wrere  no  clearance.  But  as  this  is 
not  generally  the  case,  we  make  provision  for  it  by  multiply- 

AB 
ing  the  total  displacement  per  minute  by  the  ratio,  -=     =  x, 


r    A  AT— 

as  shoxvn  in  Fig.  260,  which  gives  -         -  as  the  actual  volume 

144 

per  minute. 

To  find  the  equivalent  weight  of  this  volume,  multiply  by 
the  weight  w  of  a  cubic  foot  of  air*  as  found  in  the  table  on 
page  320.  This  makes  the  weight  of  air  per  minute  W  •=. 
LA  Nxw 


144 


*  At  the  temperature  of  the  intake  air. 


334 


PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


INDICATORS    AND    INDICATOR-CARDS. 

The  ordinary  steam-engine  indicator  may  be  used  in  deter- 
mining the  conditions  of  pressure,  etc.,  in  the  compressor 
cylinder  as  in  the  steam-engine.  The  accompanying  cards 
were  taken  by  the  author  from  a  steam-driven  single-stage 
and  single-acting  air-compressor. 

The  card,  Fig.  259,  was  from  the  steam  end  and  the  card, 
Fig.  260,  from  the  air-cylinder.  A  represents  the  beginning 


FIG.  260. — Card  taken  from  the  Air-cylinder  of  an  Air-compressor. 

of  the  stroke  of  each  piston,  the  distance  EA  representing 
atmospheric  pressure,  14.7  Ibs. 

As  the  stroke  advances  the  pressure  in  the  air-cylinder 
becomes  greater  as  indicated  by  the  line  AC,  which  is  called 
the  compression  line.  When  the  point  C  is  reached  the  com- 
pressed air  is  released  (delivered)  from  the  compressor  into  the 
receiver;  /^represents  practically  the  pressure  in  the  receiver. 
At  D  the  end  of  the  stroke  is  reached  and  the  return  stroke, 
during  which  admission  is  occurring,  the  pressure  being  re- 
duced to  atmospheric  pressure  as  shown  by  the  line  of  admis- 
sion BA.  By  comparing  Figs.  259  and  260  the  opposite  con- 
ditions of  pressure  in  the  steam-  and  air-cylinders  are  made 
manifest. 

Horse-power  of  Air-compressor. — To  find  the  horse-power 
from  the  indicator-card,  the  same  general  method  is  employed 
as  for  the  steam-engine,  that  is,  of  finding  the  mean  height  of 


COMPRESSED  AIR. 


335 


the  card,  either  by  use  of  a  planimeter  or  by  ordinates,  then 
multiplying  by  the  scale  of  the  indicator-spring,  which  gives  Pe, 
the  mean  effective  pressure.  This  may  then  be  placed  in  the 


• 


FIG.  261. — Air-heater. 
PLAN 

formula  -         -  =  H.P.      By  finding  from  the  cards  the  H.P 
33*000 

of  both  steam  and  air  ends  the  friction  in  the  machine  may 
be  determined.  The  air-card  will  give  somewhat  less  H.P. 
than  the  steam-card,  the  difference  being  due  to  friction. 


336  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

Freezing  of  the  ExJiaust  in  Air -motors. 

A  great  deal  has  been  said  in  the  foregoing  upon  the  fact 
that  air  when  compressed  rapidly  attains  an  increase  of  tem- 
perature, for  which  reason  jacketed  cylinders  and  intercoolers 
are  used  in  connection  with  the  compressor.  On  the  other 
hand,  when  air  is  expanded,  as  is  the  case  in  any  motor,  there 
is  a  corresponding  lowering  of  the  temperature.  Now,  if  the 
highly  compressed  air  reaches  the  motor  cool,  as  it  is  likely  to 
do  after  passing  through  long  lines  of  piping,  and  if  the  air 
contains  moisture,  the  expansion  will  cause  the  exhaust  to 
have  such  a  low  temperature  that  the  exhaust-pipe  is  liable  to 
become  clogged  by  ice.  In  fact,  quite  a  great  deal  of  trouble 
is  experienced  in  this  manner.  One  way  to  obviate  this  is  to 
extract  all  the  moisture  from  the  air  before  it  reaches  the 
motor,  or  at  least  as  much  as  possible.  This  can  be  done  by 
placing  two  receivers  between  the  compressor  and  the  motor, 
one  near  each.  The  receiver  near  the  compn^ssor  catches  the 
free  moisture,  and  the  second  one  drains  all  the  water  which 
has  been  condensed  in  the  pipe. 

Another  very  practical  method  is  to  heat  the  air  close  to 
the  point  of  its  admission  to  the  motor.  By  this  means  the 
range  of  temperature  which  is  required  for  a  given  number  of 
expansions  is  made  high  enough  so  that  the  temperature  of  the 
exhaust  will  be  above  freezing.  Fig.  261  shows  a  reheater 
made  by  the  Rand  Drill  Company.  The  air  enters  it  at  the 
top  and  leaves  it  at  the  bottom.  The  air-chamber  has  a  conical 
shape  which  allows  for  the  increase  of  volume  of  the  air  as  it  is 
heated.  By  this  means  the  velocity  of  the  air  is  not  retarded. 

FRICTION    OF    AIR    IN    PIPES. 

In  an  ordinary  steam-plant,  it  is  usual,  in  determining  the 
quantity  of  steam  required,  to  find  the  horse-power  of  the 
engine  and  then  arrange  to  supply  the  steam  to  develop  that 
horse-power.  In  compressed-air  systems  the  motor  often  is 
so  far  away  from  the  source  of  pressure  that  a  great  loss  of 
pressure  is  sustained  by  the  air  in  passing  from  one  to  the  other 


COMPRESSED  AIR. 


337 


by  friction  of  the  air  in  the  pipes,  especially  if  there  are  many 
sharp  turns  in  the  pipe.  The  difference  found  by  subtracting 
the  pressure  of  the  air  entering-  the  motor  from  the  air  leaving 
the  compressor  is  called  the  '  '  difference  of  head.  '  '  The  fol- 
lowing formula,  given  by  Mr.  Frank  Richards,  gives  the  extra 
head  required  to  overcome  the  friction  in  the  pipes: 


in  which  D  =  diameter  of  pipe  in  inches  ; 
L  =  length  of  pipe  in  feet  ; 

V  •=.  volume  of  air  delivered  in  cubic  feet  per  minute; 
H  '=  head  or  difference  of  pressure  required  to  over- 

come friction  and  maintain  the  flow  ; 
a  =  constant,   whose  value  is  found  experimentally 
for  different  sizes  of  pipe. 

VALUES  OF   '  '  a  "  FOR  DIFFERENT  DIAMETERS  OF  WROUGHT- 

IRON   PIPE. 

........  934 


ij" 

...    .5 

li" 

.662 

2" 

.565 

2i" 

.    -65 

3"  .    ... 

•  73 

&"'• 

.    .787 

4".  . 

.84 

5" 

6", 

8" 
10". 

12". 

16", 

20". 

24". 


.125 

.2 

.26 

•34 
•4 

•45 


The  above  formula  may  also  be  made  use  of  for  calculating 
the  size  of  pipe  required.  For  this  use,  however,  the  handling 
of  the  fifth  root  of  D  becomes  very  inconvenient.  It  is  best  to 
use  logarithms  or  to  find  a  table  of  fifth  powers,  and,  if  neces- 
sary, interpolate. 

PROBLEMS. 

1.  Find   the  total   piston-displacement    (volume  swept  over   by 
the  piston)  per  minute  of  a  single-acting  one-stage  air-compiessor 
making  150  revolutions  per  minute,  the  stroke  being  12  inches,  diam- 
eter of  piston  10  inches.     Piston  rod  i£  inches. 

2.  Find  the  volume  in  cubic  feet  of  the  air  required  for  a  double- 


33$  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

acting  two-stage  compressor  making  100  revolutions  per  minute,  the 
stroke  being  24  inches,  the  diameter  of  the  intake  or  low-pressure 
air-cylinder  20  inches,  and  the  clearance  2  per  cent.  Piston  rod  3 
inches. 

3.  Find  the  volume  in  cubic  feet  of  the  air  required  for  a  double- 
acting  compressor  of  the  two-stage  type  making   100  revolutions  per 
minute,  the  stroke  being  12  inches,  the  diameter  of  the  piston  being 
8  inches,  and  from  which  the  card  shown  in  Fig.  260  was  taken. 

4.  Reproduce  the  indicator-card  shown  in   Fig.  259  on  tracing- 
paper,  and  find  the  indicated  horse-power  of  the  steam  end  of  the  com- 
pressor from  which  it  was  taken,  the  stroke  being  12  inches,  bore  of 
cylinder  8  inches,  revolutions  125  per  minute,  and  scale  of  spring  55. 

5.  Reproduce,  as  in  the  above  problem,  the  indicator-card  (Fig. 
260)  from  the  air-cylinder  (single-acting)  of  the  compressor,  the  stroke 
being  12  inches,  bore  of  cylinder  8  inches,  scale  of  spring  60,  revo- 
lutions per  minute  125.      Find  the  indicated  horse-power  of  the  air- 
cylinder.     Piston  rod  ij  inches. 

6.  From  the  results  found  in  the  above  two  problems  find  the  H.P. 
of  the  steam-cylinder  lost  in  friction.     Also  the  per  cent  of  the  in- 
dicated horse-power  of  the  steam-cylinder  lost  in  friction.     Also  de- 
termine the  efficiency  of  the  machine. 

7.  Let  the  air  furnished  by  the  compressor  in  problem  2   be  led 
through  a  lo-inch  pipe  a  distance  of  4  miles  to  a  motor.       Find  the 
extra  pressure  in  Ibs.  per  square  inch  required  to  overcome  the  friction. 

8.  Find  the  weight  of  air  compressed  per  minute  in  problem  3, 
the  temperature  of  the  intake  air  being  90°. 


CHAPTER    XXVII. 
HOT-AIR   ENGINES. 

HOT-AIR  engines,  as  the  name  indicates,  use  air  for  the 
working-fluid.  The  working  effect  is  produced  by  the  alternate 
heating  and  cooling  of  a  body  of  air. 

The  air  on  one  side  of  a  piston  is  suddenly  heated,  causing 
it  to  expand  and  drive  the  piston  forward. 

After  it  has  expanded  it  is  cooled  and  contracted  by  some 
external  means,  after  which  it  is  heated  and  expanded  again. 
Fig.  262  shows  a  sectional  view  and  Fig.  263  an  elevation  of 
an  Ericson  Hot-air  Engine. 

In  the  sectional  view  2  is  the  power-piston  working  in  the 
cylinder  marked  i,  which  is  open  at  the  top. 

3  is  another  piston  of  very  large  volume  used  to  transfer 
the  air  from  above  it  to  below  it  and  vice  versa.  6  is  a 
gas-burner  which  heats  the  lower  end  of  the  cylinder  shown 
at  4. 

17  is  a  water-pump  whose  piston  is  operated  by  the  engine. 
The  power-piston  2  and  the  transfer-piston  3  transform  their 
reciprocating  motion  to  rotary  motion,  the  former  through  the 
crank-beam  8  and  the  latter  through  the  bell-crank  12,  better 
shown  in  the  elevation,  Fig.  263. 

The  piston-rod  of  the  transfer-piston  passes  through  the 
hollow  piston-rod  of  the  power-piston. 

The  upper  end  of  the  cylinder  is  jacketed  so  that  the  water 
which  is  pumped  all  passes  out  through  it,  keeping  that  end 
of  the  cylinder  cool  all  the  time. 

The  lower  end  of  the  cylinder  is  surrounded  with  A  non- 
339 


340  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 


FIG.  262. — Hot-air  Engine. 


HOT -AIR  ENGINES. 


34i 


conductor  of  heat  so  that  it  is  kept  at  a  high  temperature  all 
the  time. 

The  transfer-piston  does  not  fit  tight  in  the  cylinder,  but 


FlG.  263. —  Hct-air  Engine. 

leaves  a   space   around  it  through  which   the   air  may  pass  to 
and  fro. 

The  operation  is  as  follows :  The  lower  end  of  the  cylinder 
is  first  heated  by  the  gas-burner.  The  engine  must  be  started 
by  giving  it  a  revolution  or  two  by  hand. 


342  PUMPS,  GAS-ENGINES,  WATER-POWER,  ETC. 

The  air  contained  in  the  cylinder  is  first  compressed  in  the 
cool  top  part,  the  pistons  approaching  each  other. 

This  compression  causes  the  cool  air  to  pass  by  the  trans- 
fer-piston to  the  bottom  of  the  cylinder,  where  it  is  heated  and 
immediately  expands,  driving  the  power-piston  upward ;  the 
fly-wheel  carries  the  motion  to  where  the  expansion  by  the 
heat  gives  the  piston  another  impulse. 

It  is,  plainly,  single-acting. 

An  attachment  may  be  used  which  will  burn  wood  or  other 
solid  fuel  instead  of  gas. 

This  engine  is  only  used  where  small  quantities  of  power 
are  required,  the  running  of  small  pumps  being  its  principal 
application. 

It  is  especially  suited  to  pumping  because  of  its  compara- 
tively low  speed.  The  low  speed  is  due  to  the  fact  that  it 
takes  some  time  for  the  heat  to  impart  its  expansive  effect  to 
the  body  of  air.  The  same  air  is  used  continuously,  and  is 
cooled,  compressed,  heated,  and  expanded  in  the  regular  order 
with  little  noise. 

CAPACITY. 

PLAN 

The   horse-power  is   found    by  the    formula,    -        — -,   the 

33,000 

same  as  for  the  steam-engine,  P  being  obtained  from  an  indi- 
cator-card taken  from  the  air-cylinder. 

C. 


FIG.  264. 

The  card  shown  in  Fig.  264  was  taken   from  an  Ericson 
Hot-air  Engine. 

AB  is  the   atmospheric-pressure  line.      CB  is  the  line  of 


HOT-AIR  ENGINES.  343 

high  pressure  due  to  heating  of  the  air  in  the  lower  end  of  the 
cylinder  and  made  while  the  power-piston  is  moving  upward ; 
it  is  noticeable  that  the  end  at  B  is  lower  than  the  atmospheric 
line,  showing  that  the  air  expanded  to  a  pressure  lower  than 
atmospheric  pressure.  BDC  is  made  during  the  downward 
stroke  of  the  power-piston,  showing  the  gradual  compression 
of  the  air.  Hence  CB  may  be  called  the  expansion-line  and 
BDC  the  compression-line. 

PROBLEMS. 

1.  Trace  the  card  shown  in  Fig.  264,  andfmd.the  indicated  horse- 
power developed,  the  revolutions  per  minute  being  47,  the  bore  of 
the  air-cylinder  8  inches,  the  stroke  of  the  air-piston  4  inches,  and  the 
scale  of  the  indicator-spring  10. 

2.  A  pressure-gauge  on  the  discharge-pipe  of  the  water-cylinder  in 
the  above  test  showed  a  pressure  of  32  Ibs.  per  square  inch.     The 
diameter  of  the  water-piston  is  if  inches,  and  its  stroke  is  9  inches. 
Find  the  number  of  foot -Ibs.  of  work  done  per  minute  by  the  water- 
piston,  remembering  that  the  water-pump  is  double-acting. 

3.  Find  the  horse-pDwer  lost  in  friction,  leakage,  etc. 

4.  What  is  the  efficiency  of  the  machine  from  the  conditions  giver. 
in  the  previous  problems  ? 


344 


TABLE  I. 


PROPERTIES    OF    SATURATED    STEAM. 


rt 

i 

Total  Heat 

2^ 

~S 

Vacuum  Gaug 
Inches  of  Me 
cury. 

Absolute  Press 
ure,  Ibs.  per 
square  inch. 

2--S 
5.3 
g§ 

fl 

above  32°  F. 

Latent  Heat  L 
=  H-  h. 
Heat-units. 

Relative  Volun 
Vol.  of  Watei 
at  39°  F.  =  1. 

Volume.  Cu.  f 
in  lib.  of  Steal 

Weight  of  1  cu, 
ft.  Steam,  Ib, 

In  the 
Water 
h 
Heat- 
units. 

In  the 
Steam 
H 
Heat- 
units. 

29.74 

.089 

32 

0 

1091.7 

1091.7 

208080 

3333.3 

.00030 

29.67 

.122 

40 

8. 

1094.1 

1086.1 

154330 

2472.2 

.00040 

29.56 

.176 

50 

18. 

1097.2 

1079.2 

107630 

1724.1 

.00058 

29.40 

.254 

60 

28.01 

1100.2 

1072.2 

76370 

1223.4 

.00082 

29.19 

.359 

70 

38.02 

1103.8 

1065.3 

54660 

875.61 

.00115 

28.90 

.502 

80 

48.04 

1106.3 

1058.3 

39090 

635.80 

.00158 

28.51 

.692 

90 

58.06 

1109.4 

1051.3 

29290 

469.20 

.00213 

28.00 

.943 

100 

68.08 

1112.4 

1044.4 

21830 

349.70 

.00286 

27.88 

1 

102.1 

70.09 

1113.1 

1043.0 

20623 

334.23 

.00299 

25,85 

2 

126.3 

94.44 

1120.5 

1026.0 

10730 

173.23 

.00577 

23.83 

3 

141.6 

109.9 

1125.1 

1015.3 

7325 

117.98 

.00848 

21.78 

4 

153.1 

121.4 

1128.6 

1007.2 

5588 

89.80 

.01112 

19.74 

5 

162.3 

130.7 

1131.4 

1000.7 

4530 

72.50 

.01373 

17.70 

6 

170.1 

138.8 

1133.8 

995.2 

3816 

61.10 

.01631 

15.67 

7 

176.9 

145.4 

1135.9 

990.5 

3302 

53.00 

.01887 

13.63 

8 

182.9 

151.5 

1137.7 

986.2 

2912 

46.60 

.02140 

11.60 

9 

188.3 

156.9 

1139.4 

982.4 

2607 

41.82 

.02391 

9.56 

10 

193.2 

161.9 

1140.9 

979.0 

2361 

87.80 

.02641 

7.52 

11 

197.8 

166.5 

1142.3 

975.8 

2159 

84.61 

.02889 

5.49 

12 

202.0 

170.7 

1143.5 

972.8 

1990 

31.90 

.03136 

3.45 

13 

205.9 

174.7 

1144.7 

970.0 

1846 

29.58 

.03381 

1.41 

14 

209.6 

178.4 

1145.9 

967.4 

1721 

27.59 

.03625 

Gauge 

Pressure 
Ibs.  per 

14.7 

818 

180.9 

1146.6 

965.7 

1646 

26.36 

.03794 

sq.  in. 

•M 

0.304 

15 

213.0 

181.9 

1146.9 

965.0 

1614 

25.87 

.03868 

1.3 

16 

216.8 

185.B 

1147.9 

962.7 

1519 

24.33 

.04110 

2.3 

17 

219.4 

188.4 

1148.9 

960.5 

1434 

82.98 

.04352 

3.3 

18 

222.4 

191.4 

11498 

958.3 

1359 

21.78 

.04592 

4.3 

19 

225.2 

194.3 

1150.6 

956.3 

1292 

80.70 

.04831 

5.3 

20 

227.9 

197.0 

1151.5 

954.4 

1231 

19.72 

.05070 

6.3 

21 

230.5 

199.7 

1152.2 

95S.6 

1176 

18.84 

.05308 

7.3 

22 

233.0 

202.2 

1153.0 

950.8 

1126 

18.03 

.05545 

8.3 

23 

235.4 

204.7 

.7 

949.1 

1080 

17.30 

.05782 

9.3 

24 

237.8 

207.0 

1154.5 

947.4 

1038 

16.62 

.06018 

10.3 

25 

240.0 

209.3 

1155.1 

945.8 

998.4 

15.99 

.06253 

11.3 

26 

242.2 

211.5 

.8 

944.3 

962.3  j      15.42 

.06487 

12.3 

27 

244.3 

213.7 

1156.4 

942.8 

928.8  i      14.88 

.06721 

13.3 

28 

246.3 

215.7 

1157.1 

941.3 

897.6 

14.38 

.06955 

14.3 

29 

248.3 

217.8 

.7 

939.9 

868.5 

13.91 

.07188 

15.3 

30 

250.2 

219.7 

1158.3 

938.9 

841.3 

13.48 

.07420 

16.3 

31 

252.1 

221.6 

.8 

937.2 

815  8 

13.07 

.07652 

17.3 

32 

254.0 

223.5 

1159.4 

935.9 

791.8 

12.68 

.07884 

18.3 

33 

255.7 

225.3 

.9 

934.6 

769.2 

12.32 

.08115 

19.3 

34 

257.5 

227.1 

1160.5 

9334 

748.0 

11.98 

.08346 

20.3 

35 

259.2 

228.8 

1161.0  |    932.2 

727.9 

11.66 

.08576 

21.3 

36 

260.8 

230.5 

1161.5       931.0 

708.8 

11.36 

.08806 

22.3 

87 

262.5 

232.1 

1162.0       929.8 

690.8 

11.07 

.09035 

TABLE  I. — Continued. 


345 


PROPERTIES   OF  SATURATED    STEAM. 


.  . 

Total  Heat 

2  -   . 

#?1 

Gauge  Pressun 
Ibs.  per  sq.  it 

Absolute  Press- 
ure, Ibs.  per 
square  inch. 

c-a 
32 

y 

S* 

above  32*  F. 

Latent  Heat  L 
=  H-h. 
Heat-  units. 

Relative  Volun 
Vol.  of  Wate 
at  89°  F.  =  1 

Volume.  Cu.  1 
inllb.ofstea 

Weight  of  1  cu, 
ft.  Steam,  Ib 

In  the 
Water 
h 
Heat- 
units. 

In  the 
Steam 
H 
Heat- 
units. 

23.3 

38 

264.0 

233.8 

1162.5 

928.7 

673.7 

10.79 

.09264 

24.3 

89 

265.6 

235.4 

.9 

927.6 

657.5 

10.53 

.09493 

25.3 

40 

267.1 

236.9 

1163.4 

926.5 

642.0 

10.28 

.09721 

26.3 

41 

268.6 

238.5 

.9 

925.4 

627.3 

10.05 

.09949 

27.3 

42 

270.1 

240.0 

1164.3 

924.4 

613.3 

9.83 

.1018 

28.3 

43 

271.5 

241.4 

.7 

923.3 

599.9 

9.61 

.1040 

29.3 

44 

272.9 

242.9 

1165.2 

922.3 

587.0 

9.41 

.1063 

90.3 

45 

274.3 

244.8 

.6 

921.3 

574.7 

9.21 

.1086 

31.3 

46 

275.7 

245.7 

1166.0 

920.4 

563.0 

9.02 

.1108 

82.3 

47 

277.0 

247.0 

.4 

919.4 

551.7 

8.84 

.1131 

33.3 

48 

278.3 

248.4 

.8 

918.5 

540.9 

8.67 

.1153 

84.3 

49 

279.6 

249.7 

1167.2 

917.5 

530.5 

8.50 

.1176 

86.3 

50 

280.9 

251.0 

.6 

916.6 

520.5 

8.34 

.1198 

86.3 

51 

282.1 

252.2 

1168.0 

915.7 

510.9 

8.19 

.1221 

87.3 

53 

283.3 

253.5 

.4 

914.9 

501.7 

8.04 

.1243 

38.3 

53 

284.5 

254.7 

.7 

914.0 

492.8 

7.90 

.1266 

89.3 

54 

285.7 

256.0 

1169.1 

913.1 

484.2 

7.76 

.1288 

40.8 

55 

286.9 

257.2 

.4 

912.3 

475.9 

7.63 

.1311 

41.3 

56 

288.1 

258.3 

.8 

911.5 

467.9 

7.50 

.1333 

42.3 

57 

289.1 

259.5 

1170.1 

910.6 

460.2 

7.38 

.1355 

43.3 

58 

290.3 

260.7 

.5 

909.8 

452.7 

7.26 

.1377 

44.3 

59 

291.4 

261.8 

.8 

909.0 

445.5 

7.14 

.1400 

45.3 

60 

292.5 

262.9 

1171.2 

908.2 

438.5 

7.03 

.1422 

46.3 

61 

293.6 

264.0 

.5 

907.5 

431.7 

6.92     .1444 

47.3 

62 

294.7 

265.1 

.8 

906.7 

425.2 

6.82     .1466 

48.3 

63 

295.7 

266.2 

1172.1 

905.9 

418.8 

6.72 

.1488 

49.3 

64 

296.8 

267.2 

.4 

905.2 

412.6 

6.62 

.1511 

50.3 

65 

297.8 

268.3 

.8 

904.5 

406.6 

6.53 

.1533 

51.3 

66 

298.8 

269.3 

1173.1 

9037 

400.8 

6.43 

.1555 

52.3 

67 

299.8 

270. 

.4 

903.0 

395.2 

6.34 

.1577 

53.3 

68 

300.8 

271. 

.7 

902.3 

389.8 

6.25 

.1599 

54.3 

69 

301.8 

272. 

1174.0 

901.6 

384.5 

6.17 

.1621 

55.3 

70 

302.7 

273. 

.3 

900.9 

379.3 

6.09 

.1643 

56.3 

71 

303.7 

274. 

.6 

900.2 

374.3 

6.01 

.1665 

57.3 

72 

304.6 

275.3 

.8 

899.5 

369.4 

5.93 

.1687 

58.3 

73 

305.6 

276.3 

1175.1 

898.9 

364.6 

5.85 

.1709 

59.3 

74 

306.5 

277.2 

.4 

898.2 

360.0 

5.78 

.1731 

60.3 

75 

307.4 

278.2 

.7 

897.5 

365.5 

5.71 

.1753 

61.3 

76 

308.3 

279.1 

1176.0 

896.9 

351.1 

5.63 

.1775 

62.3 

77 

309.2 

280.0 

.2 

896.2 

846.8 

5.57 

.1797 

63.3 

78 

810.1 

280.9 

.5 

895.6 

342.6 

5.50 

.1819 

64.3 

79 

810.9 

281.8 

.8 

895.0 

338.5 

5.43 

.1840 

65.3 

80 

811.8 

282.7 

1177.0 

894.8 

834.5 

5.37 

.1862 

66.3 

81 

812.7 

283.6 

.3 

893.7 

330.6 

5.81      .1884 

67.3 

82 

313.5 

284.5 

.6 

893.1 

826.8  I      5.25 

.1906 

68.3 

83 

314.4 

285.3 

.8 

892.5 

823.1         5.18 

.1928 

69.3 

84 

815.2 

286.2 

1178.1 

891.9 

319.5 

6.13     .1950 

70.8 

85 

816.0 

287.0 

.3 

891.8 

815.9 

6.07  !  .1971 

346 


TABLE  I. — Continued. 


PROPERTIES   OF   SATURATED   STEAM. 


«fl 

A 

Total 

Heat 

g. 

*»  3 

" 

s.s 

§  n« 

g®  4 

««• 

above 

32«F. 

^      o3 

=17* 

"51 

§5 

1? 

®j§'» 

11 

In  the 

In  the 

is 

!^ 

."o 

?1 

t« 

S5-* 

J—  o>  3 

0.1 

Water 
h 

Steam 
H 

s^i 

•1.2! 

o>   * 

IS 

•|i| 

,Q 

sr 

Sj^ 

Heat- 

Heat- 

"S  H  W 

*d}  ^  CJ 

*o  o 

'*«M 

S"/ 

H 

units. 

units. 

A 

a 

>"* 

£ 

71.3 

86 

816.8 

287.9 

1178.6 

890.7 

312.5 

5.02 

.1993 

72.3 

87 

317.7 

288.7 

.8 

890.1 

3G9.1 

4.96 

.2015 

73.3 

88 

318.5 

289.5 

1179.1 

889.5 

305.8 

4.91 

.2036 

74.8 

89 

319.3 

290.4 

.3 

888.9 

302.5 

4.86 

.2058 

75.3 

90 

320.0 

291.2 

.6 

888.4 

299.4 

4.81 

.2080 

76.3 

91 

320.8 

292.0 

.8 

887.8 

296.3 

4.76 

.2102 

77.3 

92 

321.6 

292.8 

1180.0 

887.2 

293.2 

4.71 

.2123 

78.3 

93 

322.4 

293.6 

.3 

886.7 

990.2 

4.66 

.2145 

79.8 

94 

323.1 

294.4 

.5 

886.1 

287.3 

4.62 

.2166 

80.3 

95 

323.9 

295.1 

.7 

885.6 

284.5 

4.57 

.2188 

81.3 

96 

324.6 

295.9 

1181.0 

885.0 

281.7 

4.53 

.2210 

82.3 

97 

325.4 

296.7 

.2 

884.5 

279.0 

4.48 

.2231 

83.3 

98 

326.1 

297.4 

.4 

884.0 

276.3 

4.44 

.2253 

84.3 

99 

326.8 

298.2 

.6 

883.4 

273.7 

4.40 

.2274 

85.3 

100 

327.6 

298.9 

.8 

882.9 

271.1 

4.36 

.2296 

86.3 

101 

328.3 

299.7 

1182.1 

882.4 

268.5 

4.32 

.2317 

87.3 

102 

329.0 

300.4 

.3 

881.9 

266.0 

4.28 

.2339 

88.3 

103 

329.7 

301.1 

.5 

881.4 

263.6 

4.24 

.2360 

89.3 

104 

330.4 

301.9 

.7 

880.8 

261.2 

4.20 

.2382 

90.3 

105 

831.1 

302.6 

.9 

880.3 

258.9 

4.16 

.2403 

91.3 

106 

331.8 

303.3 

1183.1 

879.8 

256.6 

4.12 

.2425 

92.3 

107 

332.5 

304.0 

.4 

879.3 

254.3 

4.09 

.2446 

93.3 

108 

333.2 

304.7 

.6 

878.8 

252.1 

4.05 

.2467 

94.3 

109 

333.9 

305.4 

.8 

878.3 

249.9 

4.02 

.2489 

95.3 

110 

334.5 

306.1 

1184.0 

877.9 

247.8 

3.98 

.2510 

96.3 

111 

335.2 

306.8 

.2 

877.4 

245.7 

3.95 

.2531 

97.3 

112 

335.9 

307.5 

.4 

876.9 

243.6 

3.92 

.2553 

98.3 

113 

336.5 

308.2 

.6 

876.4 

241.6 

3.88 

.2574 

99.3 

114 

337.2 

308.8 

.8 

875.9 

239.6 

8.85 

.2596 

100.3 

115 

837.8 

309.5 

1185.0 

875.5 

237.6 

3.82 

.2617 

101.3 

116 

338.5 

810.2 

.2 

875.0 

235.7 

3.79 

.2638 

102.3 

117 

339.1 

810.8 

.4 

874.5 

233.8 

8.76 

.2660 

103.3 

118 

839.7 

811.5 

.6 

874.1 

231.9 

3.73 

.2681 

104.3 

119 

840.4 

812.1 

.8 

873.6 

230.1 

8.70 

.2703 

105.3 

120 

841.0 

812.8 

.9 

873.2 

228.3 

8.67 

.2724 

106.3 

121 

841.6 

313.4 

1186.1 

872.7 

226.5 

8.64 

.2745 

107.3 

123 

842.2 

314.1 

.3 

872.3 

224.7 

3.62 

.2766 

108.3 

123 

342.9 

814.7 

.5 

871.8 

223.0 

3.59 

.2788 

109.3 

124 

843.5 

815.3 

.7 

871.4 

221.3 

8.56 

.2809 

110.3 

125 

844.1 

8160 

.9 

870.9 

219.6 

8.53 

.2830 

111.3 

126 

844.7 

816.6 

1187.1 

870.5 

218.0 

8.51 

.2851 

112.3 

127 

345.3 

817.2 

.3 

870.0 

216.4 

3.48 

.2872 

113.3 

128 

345.9 

317.8 

.4 

869.6 

214.8 

3.46 

2894 

114.8 

129 

846.5 

318.4 

.6 

869.2 

213.2 

3.43 

.2915 

115.3 

130 

847.1 

319.1 

.8 

868.7 

211.6 

3.41 

.2936 

116.3 

131 

347.6 

319.7 

1188.0 

868.3 

210.1 

3.38 

.2957 

117.8 

132 

348.2 

820.3 

.2 

867.9 

208.6 

3.36 

.2978 

118.3 

133 

348.8 

320.8 

.3 

867.5 

207.1 

3.33 

.3000 

110.3 

134 

349.4 

321.5 

.5 

867.0 

205.7 

3.31 

.3021 

347 


TABLE  I. — Continued. 

PROPERTIES  OF  SATURATED  STEAM. 


139 


140.3 


858.7 


190.9 
189.7 
188.5 
187.3 
186.1 

184.9 
183.7 
182.6 
181.5 
180.4 

179.2 


.3379 
.3400 
.34*1 
.9443 

.3463 


TABLE  II. 

TABLE    FOR   WEIRS.* 


Inches  Depth 
on  Weir. 

o 

i 

i 

i 

i 

1 

1 

i 

0.40 

O-47 

0.56 

0.65 

O.  74 

O.8l 

O   Q7 

I    O7 

o 

I  .  14 

1.25 

1.36 

1.47 

1  .  5Q 

1.  71 

I    84 

I    Q6 

2   OQ 

2  .  12 

2    36 

2.60 

2    64 

2    78 

2Q<J 

-i    ofi 

**    22 

l.-?8 

a    5-1 

•?.6q 

1  8; 

4OI 

4T7 

J.UU 

4.51 

4.68 

4.85 

5.02 

C    25 

5.18 

5    56 

•  J3 

5TJ. 



6..  

5-Q2 

6.  10 

6.30 

6.49 

6.68 

6.87 

7   O7 

727 

7.46 

7   67 

7   87 

8  O7 

8  28 

8    4O 

8  70 

8    QI 

Z 

Q    12 

9.0-3 

9.   55 

9.  77 

9.  QQ 

IO    21 

TO    J.7 

10  66 

10.88 

II      II 

II.  14 

II.  57 

II    8O 

I2-O4 

12    27 

12    75 

J^.  15 

13.  21 

1-3.47 

la.  72 

I  -5    06 

14    21 

Mj.6 

14-71 

M.q6 

15.21 

15.46 

15.72 

1C  .08 

1  6    24 

16  J.Q 

16  76 

17   O2 

17.28 

17    ce 

17   82 

18  08 

18  as 

18  62 

T-J 

18  89 

IQ    17 

IQ   44 

IO.72 

2O  OO 

2o.  27 

20    56 

20  81 

21    12 

21    40 

21.68 

21.  07 

22    26 

22.  55 

22    83 

2-J    42 

2*2,.  71 

24.01 

24.  10 

24.60 

24.  .  QO 

25    IQ 

*o-  LJ 

2C    CQ 

!6             

25.  8O 

26.  10 

26.41 

26.  71 

27.02 

27.  "}2 

27    6l 

27    QJ. 

28.26 

28.57 

28.88 

29.  19 

29.  51 

20-8^ 

-JQ    14 

•JQ   46 

18  . 

1O.7S 

31.11 

31.43 

31.75 

32.07 

32.40 

•12.  7-1 

<i-i  ,O5 

*  This  table  gives  the  number  of  cu.  ft.  per  minute  that  will  pass  over 
a  weir  i  inch  wide,  and  from  i  inch  to  iS|  inches  deep.  For  instance,  a 
weir  I  inch  wide  and  io|  inch^«  1-*ep  will  pass  13.15  cu.  ft.  of  water  per 
minute. 


348 


TABLES. 


11 


£    s. 


s?  hr 


O    |    VO     I     10    I    00 


ilWJfU 


ff\  X 


£         & 


81     § 


*    5-    ^    ?> 


vS        vg^ 


i   Sli 


2   I  °2.  I    0   i    0    I  oo   I    •*      o 

JU  R     P;     5-     5-     3     5= 


S  I  ^1  S  I  cS 

ro       TT       «o       ^ 


im*JJf«UJ  8l*|*|  *|4 


&          5     g 


r>       fj 


TABLES. 


349 


TABLE  IV. 

VELOCITY    OF   WATER. 

Table  giving  velocity  of  water,  in  feet  per  second,  and  the  cubic  feet 
of  water  per  minute,  to  develop  one  horse-power  at  80  per  cent  duty  under 
beads  from  i  to  108  feet. 


Head. 

Velocity. 

Cubic  Ft. 

Head. 

Velocity. 

Cubic  Ft. 

Head. 

Velocity. 

Cubic  Ft. 

I 

8.02 

661.765 

37 

48.78 

17.886 

73 

68.53 

9-065 

2 

"•34 

330.883 

38 

49-44 

17.415 

74 

69.00 

8.943 

3 

13.89 

220.589 

39 

50.09 

16.968 

75 

69.46 

8.822 

4 

16.04 

l65.44I 

40 

50.72 

16.544 

76 

69.92 

8.707 

5 

17.92 

i32-353 

41 

51-35 

16.  141 

77 

70.38 

8-594 

6 

19.65 

x  10.  294 

42 

51.98 

15.756 

78 

70.84 

8.484 

7 

21.22 

94.538 

43 

52.59 

15-390 

79 

71.29 

8-377 

8 

22.68 

82.720 

44 

53-20 

15-040 

80 

71.74 

8.272 

9 

34.06 

73.529 

45 

53-80 

14.706 

81 

72.19 

8.170 

10 

25-36 

66.177 

46 

54-40 

14.368 

82 

72.63 

8.070 

ii 

26.60 

60.160 

47 

54-99 

14.080 

83 

73.07 

7-973 

12 

27.78 

55-147 

48 

55-57 

13-787 

84 

73.51 

7-878 

'3 

28.92 

50.905 

49 

56.14 

I3-505 

85 

73-95 

7.785 

14 

30.01 

47.269 

50 

56.71 

13.236 

86 

74-38 

7-695 

15 

31.06 

44.118 

5i 

57.27 

12.976 

87 

74.81 

7.606 

16 

32.08 

41-360 

52 

57.84 

12.726 

88 

75.24 

7-520 

17 

33-07 

38.927 

53 

58.39 

12.486 

89 

75.67 

7.436 

18 

34-03 

36.765 

54 

58.93 

12.255 

90 

76.09 

7.353 

19 

34.96 

34-830 

55 

59.48 

12.032 

91 

76.51 

7.272 

20 

35-87 

33.088 

56 

60.  01 

11.817 

92 

76-93 

7-193 

21 

36.75 

3I.5I3 

57 

60.56 

11.610 

93 

77-35 

7.116 

22 

37.61 

30.080 

58 

61.08 

11.410 

94 

77.76 

7.040 

23 

38.46 

28.772 

59 

61.61 

ii.  216 

95 

78.18 

6.966 

24 

39.29 

27-574 

60 

62.12 

11.029 

96 

78.59 

6.893 

25 

40.10 

26.471 

61 

62.71 

10.849 

97 

79.00 

6.822 

26 

40.89 

25.453 

62 

63-15 

10.674 

98 

79.40 

6-753 

27 

41.67 

24.510 

63 

63.66 

10.504 

99 

79-8i 

6.685 

28 

42.44 

23-634 

64 

64.16 

10.340 

100 

80.22 

6.618 

29 

43-19 

22.819 

65 

64.66 

10.181 

101 

80.  61 

6-552 

30 

43-93 

22.059 

66 

65.16 

10.027 

102 

81.01 

6.487 

31 

44.65 

21-347 

67 

65-65 

9.877 

103 

81.40 

6.425 

32 

45-37 

20.680 

68 

66.14 

9-732 

104 

81.80 

6.363 

33 

46.07 

20.053 

69 

66.62 

9-591 

105 

82.19 

6.303 

34 

46.77 

19.464 

70 

67.  ii 

9-454 

106 

82.58 

6.243 

35 

47.45 

18.908 

71 

67.58 

9-321 

107 

82.97 

6.185 

36 

48.12 

18.382 

72 

68.06 

9.191 

1  08 

83.35 

6.127 

INDEX. 


PAGE 

Accumulator,  pump 266 

Adiabatic  and  isothermal  expansion 332 

Addendum  of  teeth 67,  71 

Admission,  point  of 158,   191,  231,  233 

,  valves  for ««..» 226 

Air-cushion  under  belts 57 

"  -chamber 259 

"  ,  compressed,  uses  of 319 

"  -compressors,  classification  of 320 

"  -compressor,  intercooler  for. 324,  325 

"  ,  temperature  of  compressed 324,  325 

"  -receiver 324,  326,  335 

"  ,  moisture  in 327,  336 

"  -motors,  freezing  of  the  exhaust  in 335 

327 

"  -pressures,  laws  of 329 

,  diagram  of 331 

"  ,  proper  temperature  of,  for  compressors 333 

"  -intake 332 

"  -reheater 335 

"  ,  friction  of,  in  pipes 336,  33  7 

"  -lift 271 

Babcock  and  Wilcox  boiler 121 

Ball-bearing 29 

Babbitt  metal 38 

Back-pressure 170,  180,  206 

Balancing-pulleys 48 

Bed  of  engine. 168 

Bearings  of  high-speed  engines 173 


352  INDEX. 

PACK 

Bearings,  cast  iron 38 

"         ,  classes  of 26 

"         ,  length  of 30 

"         ,  brass  or  bronze 39 

"         ,  surface  of 31,  162 

Belt  gearing 54 

"   -driven  air-compressor 322 

Bed  of  engine 168 

Bevel-gears 68,   103,  282 

Bilgram  gear-cutter 68 

Blow-off  pipe 130,  148,  151 

Blower 133 

"        plant o 134 

Boilers 116 

Boiler,  fire-tube 117 

14     ,  internally  fired 120 

"     ,  externally     "   117 

"     ,  water-tube I2I»  126 

"     ,  hanging  the • 130 

"     ,  battery  of 128 

"       accessories 142 

Bolts 80 

Bridge  wall 129 

"        in  valve-seat 167 

Brake,  Westinghouse  air 328 

Brasses 163 

Breeching 133 

Bracket-bearing 29 

Buckeye  engine , 173 

Built-up  bearing 29 

Burner,  oil 141 

Butt-joint 59 

Cams 2,  7,  84,  289 

Cam-shaped  pulley 50 

"   -shaft , 282,  287 

Cast  gears 68 

Carriage-bolt 80 

Cap-screw 81 

Centrifugal  governor 290 

force  in  belts 56 

Chimney 116,  131 

"        ,  formulas  for  height  of 132 

Chimney-gases,  heat  utilized 148 

Circular  pitch •  •  •  •  67 

Clearance  of  teeth •  •  •  69 


INDEX. 


PAGE 

Clearance  in  rotary  engines  ........................................    243 

"  engine-cylinder  ..............  .  ....................  I7o?    j^- 

""         ,  harmful  effects  of  ...........................    ..........    IOO 

•ratio  ...........................  .  ....................  I00>    203 

from  indicator  card  ........................................    jgo 

Clutch  ...........................................................      22 

Compound  engines  ...........................................  154,  196 

"       ,  tandem  and  cross  .............................    197 

"       ,  losses  in  ......................................    198 

"       ,  advantages  of  ................................    199 

"       ,  objections  to  .................................    199 

"       ,  ratio  of  cylinders  ........  .............  200,203,    325 

"  "       ,  receiver  of  ...................................    200 

engine  indicator-cards  .................  201,202,203,  2O4>    2°5 

Collars  for  shafting  ..........................................     18,      28 

Collar-bearing  ...............................................     26,     3  1 

Cone-pulleys  ..............................................  '  .......      49 

"       ,  design  of  ...........................................      52 

Conical  pulleys  ...................................................      49 

Condensers  ...................................................  i  54,   206 

"  ,  vacuum  in  ...........................................    207 

"  ,  jet  ..............................................  207,    208 

,  surface  ..........................................  207,    209 

"  ,  tubes  of  surface  .....................................    208 

,  jet  and  surface  compared  .............  ................    210 

Condenser  plant  ..................................................    212 

tube-joints  ...........................................    213 

"         ,  belt-driven  and  independent  ........  ....................    214 

"          ,  siphon  .................................................    217 

Condensing  water,  methods  of  cooling  ............................    210 

Cooling-tower  ....................................................    210 

Coefficient  of  friction  .........................    .  ..34,  35,    36,   37,  38,    165 

Compressed  air  for  oil  feed  .......................................    139 

Compression,  point  of  ............................  ............    158,  191 

line  ....................  ,  ............  ........   191,  333,  343 

Compressors  .....................................  ............  271,  324 

Coal,  classification  of.  .  ...........................  ................    137 

Charcoal  ........................................................    138 

Coke  ..............................................  i  ..............    138 

Coking  system  of  firing  ...........................................    138 

Combustion,  rate  of  ..............................................    135 

"  ,  air  required  for  ....................................  ..    157 

Connecting  rod  ......................................  155,  160,    162,    282 

",  diameter  of  ........................  ,  .............    162 

"    ends...  ......................................  ......    163 

Concrete  foundation  for  engines  ......................  .  ............  _  138 

Conical  linkwork  .................................................    103 


354  INDEX. 

TAG* 

Cornish  boiler . 121 

Counter-shaft 16 

Couplings 21,  22 

Corliss  valves 226 

"            "     ,  releasing  gear  of 228 

Corliss  engine 177 

Cranes , 92 

Crank 155,  163 

"      -shaft,  diameter  of 161 

Cross-head 155,  159,   160,  161,  282 

pin,  dimensions  of. 161 

"           guides 162 

Crowbar 99 

Crank,  forged , 163 

"     ,  disk 163 

"     ,  overhanging 164 

"     -pin,  dimensions  of 164 

"     -shaft  for  direct-connected  dynamo 166 

Crown  of  pulleys 48 

Curve  of  cam 85 

"       "       ".  to  find 86,  88 

Cut-off,  point  of 173,  190,  196 

"        and  compression,  equalizing 221 

"     ,  varying  the 221 

"     ,  manner  of  changing,  in  Corliss  engine 229 

"     ,         "        "         "            "    Greene      " 230 

"     ,  effect  on,  of  changing  travel  or  angle  of  advance. .. 230 

Cut  gears 68 

Cycle  of  engine. 158 

Cylinder,  names  of,  in  multiple-expansion  engines 196 

"       ,  formula  for  thickness 158 

"       -head 159 

"       ,  manner  of  connecting  to  bed 168 

D  valve 146,  155,  156,   224,  225 

Dampers 143 

Dash-pot 180,  229 

Dead  center 101,  197,  219,  244 

Dead  plate 129,  139 

Deane  boiler  feed-pump 146 

Dedendum  of  teeth 67,    71 

Dies 80 

Diagram,  Zeuner  valve 233 

Diametral  pitch 67 

Dome,  steam , 117 

Drive-screw 82 


INDEX.  355 

PACK 

Draft 1 16 

"     ,  forced 133 

"     -gauge   132 

Drum,  steam  and  water 121 

Duty  of  pump 276 

Dynamometer 23 

Eccentric 156,  157,  167,  219 

"         ,  go-ahead 222 

,  reversing 222 

"         ,  clotted 226,  231 

"         ,  shifting 231 

"         ,  setting  of 221 

"         -strap 156,  167 

"         -rod 156,  167 

Eccentricity 156,  157,  167,  231,  233 

Economizer ; 148,  150 

Efficiency  of  machines 13 

"         ''  screw .- 75 

"   boiler 136 

,  thermal  of  steam  engine 192 

"        ,  mechanical  of  steam  engine 192,  193 

"        ,  commercial  of  steam  engine 193 

Electric  igniters 291 

Elements  in  fuels 135 

Endless  screw 76 

Energy 10 

Energy,  two  kinds  of 1 1 

"       ,  conservation  of , ir 

"       ,  sources  of 12 

Engine,  steam 154 

"      ,  single-acting 155,   341 

"      ,  double-acting 155 

"      ,  reversing 162 

"      ,  compound 196 

"      ,  multiple-expansion 1 96 

"      ,  hoisting 93 

"      ,  Corliss 226 

44      ,  Greene,  valve-gear  of 229 

**      ,  rotary 241 

44       ,  abutment  and  piston  of 24r 

44      ,  rotary,  packing  for 243: 

"      ,       "      ,  manner  of  expanding  steam  in 244 

"      ,  first 245 

44      ,  Brancas' 245 

41      ,  gas 280 

44       ,  gasoline 292 

44       ,  oil 294 


356  INDEX. 

PACK 

Engine,  water 31  It   3^ 

"       ,  steam,  appendages  to 254 

Engineer ! 

Engineering x 

Epicycloid  teeth , 68,      72 

Equation  for  flat  of  threads 78 

"    speed  of  gears 72 

"    cam 89 

"    differential  windlass 94 

pulley 95 

Equivalents  for  link  work 101,  104 

Evans'  friction  pulleys 50 

Exhaust  port 158,  167 

"         steam 159 

"         port  and  pipe,  dimensions 168 

Expansion  in  compound  engines 200 

of  tubes  in  surface  condenser 214 

"    steam  in  turbine 247,  248,  250 

and  contraction  of  tubes 120 

Expansions,  number  of 200 

Expansion,  curve 190,  191,  205,  287,  343 

'     ,  theoretical,  construction  of 190 

Fan,  forced  draft 133 

"  ,  circulating  air 21 1 

Feed- water 124,  144 

"     -pump 144,  146 

"     -water-heater 147,   148,  149 

"     -pipe 148 

Female  threads 79 

Fellows  gear-shaper 68 

Firing 138 

Fire-line 128 

Flame-bed 129 

"     -igniter 291 

Flexible  connectors 2 

Fly-wheel 102,   155,  166,  342 

,  gas-engine 284 

*'            .air-compressor 325 

Follower 85 

.flat-footed... 86 

"        .swinging 86 

path 86 

Formula  for  ropes 63 

"         "    pitch  of  gears 67 

44          "    H. P.  of  gear-teeth 73 

**         "    heating-surface 120 


INDEX.  357 

FAGK 

Formula  for  dimensions  of  chimneys x 32 

"         "    heat  required  in  furnace !^6 

"    safety-valve I44 

"         "    area  of  cross-head  slides i62 

"         "    diameter  of  crank-pin 164 

"    length       "       "         " 165 

"    diameter  of  crank-shaft 1^6 

"         "                      "    fly-wheel 166 

"         "    parts  of  engines,  note  on i  y  i 

Friction 34,  335 

"       clutch 23 

"       ,  sliding  and  rolling   29 

"       gearing 41 

"       wheels,  made  of 41 

"      ,  grooves  in 41 

"             "      connecting  intersecting  axes 43 

"      .graphics 43,  44 

"       in  cams 85 

"       of  steam  in  exhaust-pipe 170 

of  air 336 

Freezing  of  exhaust  air 334 

Fuels 135,   137,  139 

Furnace 116 

Gas,  air  required  for  combustion  of 280 

"  ,  compression  of,  in  engine 280,   282,  285,  286 

"  ,  pressures  and  temperatures  of  exploding 280 

"  ,  coal,  table  of , 280 

"  and  air  mixture  for  maximum  pressure. . . ., 281 

"  -engines,  classification 281 

"       ,  four-cycle 281 

,  two-      "      281,  284 

"       ,  Otto 281,283 

"       ,  Day 284 

"       ,  H.P.  of 287 

"           "       ,  losses  in 287 

"      ,  working  fluid 287 

"       ,  valves  for 288 

Gasoline-engines 292 

"       ,  manner  of  feeding  to  engine 292 

"       -tank,  position  of 292 

"       -engine,  Otto 293 

,  spraying  of 295 

Gauge  pressure 142,  329 

"       ,  water 142 

"      ,  vacuum. 215 


358  INDEX. 

PAGB 

Gauge  cocks 143 

Gears,  representing '  70 

Governors 170,  179,    180,   226,  229,  230 

for  high-speed  engines 230 

"            "    gas-engines , 289,  290 

"            "    gasoline-engines 293 

Grate-surface 128,  139 

"     -bar 128 

"     ,  hollow 133 

Graphite 40 

Grooves  in  bearings 32 

"         for  ropes 64 

Guides 162 

Guide-plates  in  turbine 248 

Hanger-bearing 29 

Heating-surface 117,  1 20 

Heat,  definitions , 112 

"    ,  unit  of 112 

"    ,  equivalent  of,  in  work 192 

units  in  pound  of  steam 112 

"    ,  loss  of,  in  simple  and  compound  engines 198 

"    of  exploding  gases , 287 

Head 297 

"     ,  loss  of 312,  314 

"     ,  equivalent  for,  in  pressure  per  sq.  in , 297 

Header .  .  .  121,  124 

Heine  boiler 125 

High-speed  engines 173 

H.P.  of  belts 56 

"     "   gear-teeth 73 

"     "    engine  from  indicator-card 187 

"     "        "       ,  formula  for 182,  188 

"     "    gas-engines 287 

"     "    streams 299 

Hooke's  joint 194 

Hot- well 207 

Hot-air  engines 339 

"            "         ,  operation  of 341 

.H.P.of 342 

Hydraulic  pump 311 

Igniting  apparatus 282,  289,  291 

"         tube 286 

Inertia  governor 290 

Indicator .  181 


INDEX. 


359 


PAGE 

Indicator-spring 181,  183,  187,  286 

-pencil 18 1    183 

-drum 181,  183 

-rig  for  both  ends  of  the  cylinder 183 

"          -card,  length  of !8ij 

"     ,  taking ,86 

•"    ,  data  for j86 

"  "     ,  average  height 187 

"        -cards  from  compound  engine 201 

"  "     .combining .' 202 

"  "     defective 191 

-card  from  condensing  engine 217 

"        "      gas-engine 286 

,  irregularity 286 

"     of  air-compressor ,-  .325,  333,334,  335 

"      "  hot-air  engine 341 

"      "  steam-pump 277 

Intercooler 324,  325 

Injector 139,  144,  146,  217 

,  monitor 147 

"         ,  economy  of 148 

Inverse  cam 88 

Involute  teeth 63,  72 

Jack-screw,  the 75 

Jacket-water,  heat  lost  in 287 

for  gas-,  gasoline-,  and  oil-engines 29^ 

Joints  for  rope  belting 59 

Journal  bearing 26,  3 1 

Lagging iQ8 

Laced  belt,  safe  working  tension 55 

Lacing 56,  59 

Lag-screw 81 

Lathe-treadle 50 

Lap  of  valve 218,  220 

"  ,  effect  of,  on  point  of  cut-off 220 

"  ,     "  "       "       "  compression 220 

Law  of  Charles 280,  281 

"      "  wheelwork 92 

Leather  belts 54 

-link  belt 57 

Lead 217,  219 

Lever,  the 3,  90,  289 

"      ,  weight  of 4 

"      ,  modifications  of IO 


36o  INDEX. 

PAGE 

Line-shaft 16 

Linkwork 98,  222,  226 

"  ,  advantages  of 98 

"  for  intersecting  axes 103 

Link,  Stephenson ,. 221 

"   ,  Gooch 224 

Live  steam , 1 59 

Locomotive-boiler 121 

Loose  pulley 48 

Loss  of  head,  formula 314 

"      "  heat  from  furnace 136 

Lubricator,  engine 254 

"         ,  sight-feed 255 

Lubricant , 34 

"         ,  qualities  of  a  good 39 

Lubricants  for  different  conditions 40 

Machine 2 

"         ,  law  of 4 

plant,  arranging  a 19 

bolt So 

Machinist i 

Male  threads 40 

Marine  connecting-rod 1 63 

Marriotte's  Law 158 

Main-line  shaft 1 6 

Maximum  port -opening 234 

Mason  pump-governor 2* 2 

Mean  effective  pressure , 187 

Meyer  valve 225 

Meter,  water 274 

Mineral  oils 40 

Motors,  water,  setting  of 311 

"       ,  air 327 

"       ,  water 297,  298 

Mud-drum 124,  151 

Multiple-expansion  engine 153,  171 

Non-circular  wheels 101 

Nut 7 

Oil,  as  lubricant 39 

"  ,  methods  of  applying  to  bearings 31 

' '  mixtures 40 

"  for  fuel, 139 

"  ,  harmful  effects  of,  in  feed-water 256 


INDEX.  361 

PACK 

Oil,  atomizing  and  vaporizing 294 

"  ,  spraying  of 295 

"  -engines 294 

"  "  ,  compression  in 294 

"  "  ,  fuel  for , 295 

"  -engine,  Priestman 295 

"  "  not  economical 295 

"  ,  danger  of  explosion 296 

Orifices,  flow  of  water  from 314 

Path  of  points  in  linkwork 100 

Pantograph 185 

Packing  for  rotary  engines 243 

Pelton  water-wheel 309,   311 

Petroleum 137,  138,   139 

as  fuel  in  oil-engines 295 

Piston 155,  159,  259,    282 

"      ,  built  up 159 

"      ,  grooves  in 159 

"      -rings 38,  155-159 

"      of  indicator 181 

"      ,  air 207 

"      -valve 175,  226,   227 

"      ,  power  and  transfer 337 

"      ,  double-headed 328 

"      -rod , 159 

"        "    ,  formula  for  diameter 159 

Piping  for  indicator 181 

Plant,  boiler 116 

"     for  burning  oil  fuel 141 

"     ,  turbine 306 

"     for  making  gas — .- 288 

Pop  safety-valve 144 

Port,  steam 155 

"    ,  admission  and  ignition 282,    286 

"    ,  flame 282 

Points  of  cut-off,  etc.,  on  diagram 234 

Power,  characteristics  of  motive 12 

"       ,  unit  of 14 

"      of  streams,  measuring 3i5t   3J6 

Pressure  of  exploding  gas 280 

,  unbalanced,  in  compressor 326,   334 

Pressures  in  atmospheres 33° 

Pressure,  terminal,  in  steam-cylinder 186 

,  measure  of H3>   273 

.absolute 114,   280,   329 

"         ,  diagram  of 114 


362  INDEX. 

PAGE 

Pressure- line  of  boiler 205 

Propeller  shaft , 16 

Prony  brake 24 

Pulley 7,  93 

"       ,  fixed 8 

"       ,  movable 8,  94 

Pulleys,  combinations  of < 9 

"        ,  relation  of  applied  force  to  weight 8 

44        for  the  transmission  of  power 47 

"        ,  shrinkage  in  casting : 47 

,  rules  for  speed  of 51 

"        ,  manner  of  fastening  to  shaft 47 

Pumps 257 

"        ,  feed- water 257 

"        ,  reciprocating .  .  257 

44        ,  suction 257,  258 

,  force ,  ..  -258,  259,  339 

"        ,  air .....207,210,  214 

44        .circulating  210 

"        ,  belt-driven  air 214 

44        ,  independent  air 214 

"        ,  injection,  for  siphon  condenser 217 

44        ,  working  barrel  of 258 

41        ,  air-chamber  of  force 250 

41        for  jacket-water - 296 

44        ,  deep-well f 269 

44        ,  hydraulic 269,  311 

44        ,  steam  and  power 261 

4*       .high-service 263 

4<       ,  speed  of 271 

4<        ,  capacity  of 273 

Quarter-twist  of  belt 58 

Rack  and  pinion 71,  90 

Race,  head  and  tail 303 

Reciprocating  motion 71,  84 

1 4              rods  and  bars 2 

"             engine 154 

Receiver 154,  324 

Regulation  of  engines 170,  175 

41             "  gas-engines 284,  289 

14           4<  air-compressors 327 

Reducing  motions 181,  183,  184,  185 

Release,  point  of 158,  191 


INDEX. 


363 


PAG  a 

Reversing-engine. 162 

Rock-drill 328 

Roller  bearing 29 

Rolling  contact 85,  101 

Roney  stoker 139 

Rope  driving 61 

*'    ,  materials  used  in  making 61 

"    ,  formula  for  H.P.  of 63 

Rotary  engines 154,  244 

Rubber  belting 57 

Rule  for  H.P.  of  belts 61 

Scale,  boiler , 256 

Safety  boilers 126 

Screw,  the 7,  75,  78 

"     -cutting  machines 80 

Scarf-splice 60 

Scotch  boiler 121 

Setting,  boiler 126,  128,  131 

,  battered  walls  of 128 

"       of  turbine 307 

Set-screw 82 

Separator,  steam 255 

.oil 256 

Shear 88 

Shafting 2,  16 

"         ,  materials 17 

"         ,  strains  on 18 

"         ,  speed  of 19 

"         ,  formulas  for  diameter 20 

Sight-feed  oiler 31 

Simple  engine 198 

"     ,  losses  in 154 

"     ,  advantages  of 199 

Siphon 143 

Skew-wheels 68,  103 

Sliding  contact  of  cams 85 

Slip  of  belts 51 

Solid  and  split  pulley 47 

Spindle 16 

Sprocket-wheel 54 

Spiral  of  Archimedes 87 

Spur-wheels 68 

Spreading  system  of  firing T38 

Stack 131 

Sprayer,  perfume 294 


364  INDEX. 

FACE 

Stepped  pulleys 49 

Steam,  condensation  of,  in  cylinder 198 

"     ,  different  steps  in  its  formation 114 

•'        engines,  performance  of  different  types 193 

"     ,  friction  of 200,  202,  206 

"     ,  latent  heat  of 114 

"     ,  reheating  of  exhaust 201 

"     ,  manner  of  cooling  in  condensers. 207 

"     ,  waste  of,  in  rotary  engines 244 

'     ,  consumption  of,  in  rotary  engines 244 

"     ,  condensation  of,  in  pipes 255 

"     ,  saturated 115 

"     -space 117 

"     ,  superheated 115 

"     -chest 155,  167,  241 

*'     -ports ' 167 

"       table 344 

•'         "     example  of  use  of 116 

"     -driven  air-compressor 321 

Stone-crusher 92,  142 

Stoker,  mechanical ^ 139 

Streams,  average  depth  of 315 

Stroke  of  engine 170,  1 79 

"       "       "     events  of 234 

Strut,  the  moving 91 

Stuffing-box , 54,  167,  282 

"         for  valve-rod 167 

System  of  gears 72 

Table  of  friction  coefficients 36 

"     "  H.P.  of  rope-drive 68 

Table  of  U.  S.  threads 78 

I 344 

"       II 347 

"     HI 348 

"      IV , 349 

Tandem  engine 197 

Taps So 

Tappets,  in  valve-gear 229 

Tension  in  belt. 55 

Tensile  strength  of  ropes 62 

Temperature,  absolute 113,  280,  329 

"          ,  range  of,  in  cylinder 199,  336 

of  exploding  gas 280,  286 

Thermometers 112 

Toothed  gearing 66 

Toggle-joint,  the 91 


INDEX. 


365 


PAGE 

Train  of  gears  ......................................................  72,  93 

Travel  of  valve 


.   I20 

Tube-igniters  .......................................................    291 

Tubes,  burning  out  of  ................................................    2  ,.5 

Tube-expanders  ........    ............................................    I2^ 

Turbine,  steam  ...................................................  t  ^  f  244 

"  »  high  speed  of  .........................  245,  247,  248,  249,  252 

"  ,  efficiency  of  ..........................................    245 

"  ,  advantages  of  ...................  ..................  245,  353 

"  ,  De  Laval  ............................................   247 

"  ,  Parsons  .............................................    248 

"  ,  Curtis  ...............................................    250 


252 

Turbines,  water  ..............................  .  ......................  205 

"              "     ,  mixed  flow  ........................................  300 

44        ,  runner  of  ................................................  303 

44        ,  manner  of  applying  water  ................................  302 

,  H.P.  of  ..................................................  306 

"        ,  speed  of  ................................  .................  307 

"        ,  regulation  ...............................................  307 

Vacuum  line  ...................................................  190,  191 

"      in  condenser.  ...  ...........................................  214 

gauge  .....................................................  215 

"       ,  average,  in  condenser  .....................  ...............  216 

"       between  belt  and  pulley  ...................................  51 

Valves,  classes  of  ..................................................  105 

Valve,  safety  .......................................................  143 

"     ,  back-pressure  .............................................  '  '  108 

"     .piston  .....................................................  227 

"     taking  steam  internally  ....................................  -  •  •  •  227 

"     ,  Giddings  ................................................  ....  227 

"     ,  exhaust,  for  gas-engines  ................................  282,  284 

"     ,  poppet  .................................................  288,  324 

"     for  gas-engines  ...............................................  288 

"      "4    gasoline-engines  ...........................................  292 

"      releasing-gear  of  Corliss  engine  ...............................  228 

"     of  Greene  engine  .............................................  229 

"     diagrams  ....................................................  232 

"        ,  problems  in  ....................................  ••••  239 

"     ,  steam-lap  of  ................................................  218 

14     ,  lead  of      ....................................................  219 

"     ,  pressure-plate  ...............  ...............................  220 

••      -seat  ...............  .............    ...........................  220 

"      -rod  ..........................................................  221 

-rods  for  Buckeye  engine  .......    .............................  226 

"      ,  the  Allan  ..................................................  223 

44      .double-ported   ..............................................  224 


366  INDEX. 

PAGE 

Valve,  gridiron  . . . '. 225 

"  ,  Meyer 225 

"  ,  direct. 237 

"  ,  indirect 237 

"  ,  Buckeye 226 

44  ,  Ideal  engine 226 

44  .Corliss 226,  324 

"  ,  balanced 175,  220 

14  ,  multiple-ported 175 

"  ,  friction  of,  against  seat .  175 

Variable  velocity  pulley. 50 

41  "  cam 88 

Vaporizer. 295 

Velocity  of  water  flowing  from  orifice 314 

"      315,349 

"         ratio  of  gear-wheels 45 

Volume  of  steam  per  hour  per  H.P 188 

Water-space 117,  142 

Waterfall,  power  transmitted 12 

Water,  wearing  effect  of „»;, 325 

"     ,  flow  of 349 

"     -power 297 

"     impulse  air-compressor 323 

"     -motors 298,  311 

44     -wheels 298 

Weight  of  leather , 57 

"        and  lever  safety-valve 143 

"        of  steam  per  hour  per  H.P 188,  190 

Weir 316 

Wedge,  the 6 

Wheels,  driver  and  driven 45 

Wheel  and  axle 10 

Wheelwcrk,  cranes,  etc 92 

Whitworth  screw-threads 79 

Windlass,  the  differential 93 

Wire  lacing 59 

Work 13 

Working  strain  on  belts 58 

Wooden  teeth  for  gears 68 

Wood-screw 82 

Wood,  as  fuel 13? 

Wrist-plate 180,  226,  228 

Zeuner  valve  diagrams 232- 

44          "     diagram,  geometric  properties  of 234 

"          "          "       ,  example  of  application   236- 


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Schapper's  Laboratory  Guide  for  Students  in  Physical  Chemistry 12mo,  1  00 

*  Tillman's  Elementary  Lessons  in  Heat 8vo,  1  50 

Tory  and  Pitcher's  Manual  of  Laboratory  Physi«s Large  12mo,  2  00 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  00 


LAW. 

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16mo,  mor.  5  00 

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Skeep,  5  50 


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11 


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*  Coffin's  Vector  Analysis 12mo,  2  50 

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*  Dickson's  College  Algebra Large  12mo,  1  50 

*  Introduction  to  the  Theory  of  Algebraic  Equations Large  12mo,  1  25 

Emch's  Introduction  to  Projective  Geometry  and  its  Application 8vo,  2  50 

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Halsted's  Elementary  Synthetic  Geometry 8vo,  1  50 

Elements  of  Geometry 8vo,  1  75 

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Series 12mo,  1  25 

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No.  2.  Synthetic  Projective  Geometry,  by  George  Bruce  Halsted. 
No.  3.  Determinants,  by  Laenas  Gifford  Weld.  No.  4.  Hyper- 
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Variable 8vo,  2  00 

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Woodward's  Probability  and  Theory  of  Errors 8vo,  1  00 


12 


MECHANICAL    ENGINEERING. 

MATERIALS   OF   ENGINEERING,  STEAM-ENGINES   AND    BOILERS. 

Bacon's  Forge  Practice 12mo,  $1  50 

Baldwin's  Steam  Heating  for  Buildings 12mo,  2  50 

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*  "                                       "       Abridged  Ed 8vo.  150 

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Carpenter's  Experimental  Engineering 8vo,  6  00 

Heating  and  Ventilating  Buildings 8vo,  4  00 

Clerk's  Gas  and  Oil  Engine.      (New  edition  in  press.) 

Compton's  First  Lessons  in  Metal  Working 12mo,  1  50 

Compton  and  De  Groodt's  Speed  Lathe 12mo,  1  50 

Coolidge's  Manual  of  Drawing 8vo,  paper,  1  00 

Coolidge  and  Freeman's  Elements  of  Geenral  Drafting  for  Mechanical  En- 
gineers  Oblong  4to,  2  50 

Cromwell's  Treatise  on  Belts  and  Pulleys 12mo,  1  50 

Treatise  on  Toothed  Gearing 12mo,  1  50 

Dingey's  Machinery  Pattern  Making 12mo,  2  00 

Durley's  Kinematics  of  Machines 8vo,  4  00 

Flanders's  Gear-cutting  Machinery Large  12mo,  3  00 

Flather's  Dynamometers  and  the  Measurement  of  Power 12mo,  3  00 

Rope  Driving 12ino,  2  00 

Gill's  Gas  and  Fuel  Analysis  for  Engineers 12mo,  1  25 

Goss's  Locomotive  Sparks 8vo,  2  00 

Greene's  Pumping  Machinery.      (In  Preparation.) 

Hering's  Ready  Reference  Tables  (Conversion  Factors) 16mo,  mor.  2  50 

*  Hobart  and  Ellis's  High  Speed  Dynamo  Electric  Machinery 8vo,  6  00 

Button's  Gas  Engine 8vo,  5  00 

Jamison's  Advanced  Mechanical  Drawing 8vo,  2  00 

Elements  of  Mechanical  Drawing 8vo,  2  50 

Jones's  Gas  Engine 8vo,  4  00 

Machine  Design: 

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Kent's  Mechanical  Engineer's  Pocket-Book 16mo,  mor.  5  00 

Kerr's  Power  and  Power  Transmission 8vo,  2  00 

Kimball  and  Barr's  Machine  Design.     (In  Press.) 

Levin's  Gas  Engine.     (In  Press.) 8vo, 

Leonard's  Machine  Shop  Tools  and  Methods 8vo,  4  00 

*  Lorenz's  Modern  Refrigerating  Machinery.   (Pope,  Haven,  and  Dean).. 8 vo,  4  00 
MacCord's  Kinematics;  or,  Practical  Mechanism 8vo,  5  00 

Mechanical  Drawing 4to,  4  00 

Velocity  Diagrams 8vo,  1  50 

MacFarland's  Standard  Reduction  Factors  for  Gases 8vo,  1  50 

Mahan's  Industrial  Drawing.     (Thompson.) 8vo,  3  50 

Mehrtens's  Gas  Engine  Theory  and  Design Large  12mo,  2  50 

Oberg's  Handbook  of  Small  Tools Large  12mo,  3  00 

*  Parshall  and  Hobart's  Electric  Machine  Design.  Small  4to,  half  leather,  12  50 

Peele's  Compressed  Air  Plant  for  Mines 8vo,  3  00 

Poole's  Calorific  Power  of  Fuels 8vo,  3  00 

*  Porter's  Engineering  Reminiscences,  1855  to  1882 8vo,  3  00 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  00 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  00 

Richards's  Compressed  Air 12mo,  1  50 

Robinson's  Principles  of  Mechanism 8vo,  3  00 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  00 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  00 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  00 

Sorel's  Carbureting  and  Combustion  in  Alcohol  Engines.     (Woodward  and 

Preston,) Large  12mo,  3  00 

Stone's  Practical  Testing  of  Gas  and  Gas  Meters. 8vo,  3  50 

13 


Thurston's  Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics. 

12mo,  $1  00 

Treatise  on  Friction  and  Lost  Work  in  Machinery  and  Mill  Work .  .  .  8vo,  3  00 

*  Tillson's  Complete  Automobile  Instructor 16mo,  1  50 

*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo,  1   25 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

*  Waterbury's  Vest  Pocket  Hand-book  of  Mathematics  for  Engineers. 

2|X5f  inches,  mor.  1  00 
Weisbach's    Kinematics    and    the    Power    of   Transmission.      (Herrmann — 

Klein.) 8vo,  5  00 

Machinery  of  Transmission  and  Governors.      (Hermann — Klein.).  .8vo,  5  00 

Wood's  Turbines 8vo,  2  50 


MATERIALS   OF   ENGINEERING. 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Church's  Mechanics  of  Engineering 8vo,  6  00 

*  Greene's  Structural  Mechanics 8vo,  2  50 

*  Holley's  Lead  and  Zinc  Pigments Large  12mo  3  00 

Holley  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments,  and  Varnishes. 

Large  12mo,  2  50 
Johnson's  (C.  M.)  Rapid    Methods    for    the   Chemical    Analysis    of    Special 

Steels,  Steel-Making  Alloys  and  Graphite Large  12mo,  3  00 

Johnson's  (J.  B.)  Materials  of  Construction 8vo,  6  00 

Keep's  Cast  Iron ' 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

Maire's  Modern  Pigments  and  their  Vehicles 12mo,  2  OO 

Martens's  Handbook  on  Testing  Materials.      (Henning.) 8vo;  7  50 

Maurer's  Techincal  Mechanics 8vo,  4  00 

Merriman's  Mechanics  of  Materials 8vo,  5  00 

*  Strength  of  Materials 12mo,  1  00 

Metcalf's  Steel.     A  Manual  for  Steel-users 12mo,  2  00 

Sabin's  Industrial  and  Artistic  Technology  of  Paint  and  Varnish 8vo,  3  00 

Smith's  ((A.  W.)  Materials  of  Machines 12mo,  1   00 

Smith's  (H.  E.)  Strength  of  Material 12mo, 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  00 

Part  I.      Non-metallic  Materials  of  Engineering 8vo,  2  00 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Wood's  (De  V.)  Elements  of  Analytical  Mechanics 8vo,  3  00 

Treatise  on    the    Resistance    of    Materials    and    an    Appendix   on    the 

Preservation  of  Timber 8vo,  2  00 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  00 


STEAM-ENGINES    AND   BOILERS. 

Berry's  Temperature-entropy  Diagram 12mo,  2  00 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.      (Thurston.) 12mo,  1  50 

Chase's  Art  of  Pattern  Making 12mo,  2  50 

Creighton's  Steam-engine  and  other  Heat  Motors 8vo,  5  00 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  ..  .  16mo,  mor.  5  00 

Ford's  Boiler  Making  for  Boiler  Makers 18mo,  1  00 

*  Gebhardt's  Steam  Power  Plant  Engineering 8vo,  6  00 

Goss's  Locomotive  Performance 8vo,  5  00 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy 12mo,  2  00 

Hutton's  Heat  and  Heat-engines 8vo,  5  00 

Mechanical  Engineering  of  Power  Plants 8vo,  5  00 

Kent's  Steam  boiler  Economy 8vo,  4  00 

14 


Kneass's  Practice  and  Theory  of  the  Injector 8vo,  $1  50 

MacCord's  Slide-valves 8vo,  2  00 

Meyer's  Modern  Locomotive  Construction 4to,  10  00 

Moyer's  Steam  Turbine 8vo,  4  00 

Peabody's  Manual  of  the  Steam-engine  Indicator 12mo.  1  50 

Tables  of  the  Properties  of  Steam  and  Other  Vapors  and  Temperature- 
Entropy  Table 8vo.  1  00 

Thermodynamics  of  the  Steam-engine  and  Other  Heat-engines.  .  . .  8vo.  5  00 

Valve-gears  for  Steam-engines 8vo,  2  50 

Peabody  and  Miller's  Steam-boilers 8vo,  4  00 

Pupin's  Thermodynamics  of  Reversible  Cycles  in  Gases  and  Saturated  Vapors. 

(Osterberg.) 12mo.  1  25 

Reagan's  Locomotives:  Simple,  Compound,  and  Electric.     New  Edition. 

Large  12mo.  3  50 

Sinclair's  Locomotive  Engine  Running  and  Management 12mo,  2  00 

Smart's  Handbook  of  Engineering  Laboratory  Practice 12mo,  2  50 

Snow's  Steam-boiler  Practice 8vo,  3  00 

Spangler's  Notes  on  Thermodynamics 12mo.  1  00 

Valve-gears 8vo,  2  50 

Spangler,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo  3  00 

Thomas's  Steam-turbines 8vo.  4  00 

Thurston's  Handbook  of  Engine  and  Boiler  Trials,  and  the  Use  of  the  Indi- 
cator and  the  Prony  Brake 8vo.  5  00 

Handy  Tables 8vo.  1  50 

Manual  of  Steam-boilers,  their  Designs,  Construction,  and  Operation  8vo,  5  00 

Manual  of  the  Steam-engine 2vols..  8vo.  10  00 

Part  I.     History,  Structure,  and  Theory 8vo,  6  00 

Part  II.     Design,  Construction,  and  Operation 8vo,  6  00 

Steam-boiler  Explosions  in  Theory  and  in  Practice 12mo,  1  50 

Wehrenfenning's  Analysis  and  Softening  of  Boiler  Feed-water.     (Patterson). 

8vo.  4  00 

Weisbach's  Heat,  Steam,  and  Steam-engines.     (Du  Bois.) 8vo.  5  00 

Whitham's  Steam-engine  Design 8vo,  5  00 

Wood's  Thermodynamics,  Heat  Motors,  and  Refrigerating  Machines.  .  .8vo,  4  00 


MECHANICS   PURE  AND    APPLIED. 

Church's  Mechanics  of  Engineering 8vo.  6  00 

Notes  and  Examples  in  Mechanics 8vo,  2  00 

Dana's  Text-book  of  Elementary  Mechanics  for  Colleges  and  Schools  .12mo,  1  50 
Du  Bois's  Elementary  Principles  of  Mechanics: 

Vol.    I.     Kinematics 8vo.  3  50 

Vol.  II.     Statics 8vo,  4  00 

Mechanics  of  Engineering.     Vol.    I Small  4to,  7  50 

Vol.  II Small  4to,  10  00 

*  Greene's  Structural  Mechanics 8vo,  2  50 

James's  Kinematics  of  a  Point  and  the  Rational  Mechanics  of  a  Particle. 

Large  12mo,  2  00 

*  Johnson's  (W.  W.)  Theoretical  Mechanics 12mo.  3  00 

Lanza's  Applied  Mechanics.  .  . .  \ 8vo.  7  50 

*  Martin's  Text  Book  on  Mechanics.  Voi.  I,  Statics 12mo,  1  25 

*  Vol.  II,  Kinematics  and  Kinetics.  12mo.  1   50 

Maurer's  Technical  Mechanics 8vo.  4  00 

*  Merriman's  Elements  of  Mechanics 12mo,  1  00 

Mechanics  of  Materials 8vo,  5  00 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  00 

Robinson's  Principles  of  Mechanism 8vo,  3  00 

Sanborn's  Mechanics  Problems Large  12mo,  1  50 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  00 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  00 

Principles  of  Elementary  Mechanics 12mo,  1  25 


15 


MEDICAL. 

*  Abderfialden's  Physiological  Chemistry  in  Thirty  Lectures.     (Hall  and 

Defren.) 8vo,  $5  00 

von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) 12mo,  1  00 

Bolduan's  Immune  Sera 12mo,  1  50 

Bordet's  Studies  in  Immunity.      (Gay).      (In  Press.) 8vo, 

Davenport's  Statistical  Methods  with  Special  Reference  to  Biological  Varia- 
tions  16mo,  mor.  1  50 

Ehrlich's  Collected  Studies  on  Immunity.     (Bolduan.) 8vo,  6  00 

*  Fischer's  Physiology  of  Alimentation Large  12mo,  2  00 

de  Fursac's  Manual  of  Psychiatry.      (Rosanoff  and  Collins.)..  .  .Large  12mo,  2  50 

Hammarsten's  Text-book  on  Physiological  Chemistry.      (Mandel.) 8vo,  4  00 

Jackson's  Directions  for  Laboratory  Work  in  Physiological  Cherm'stry .  .8vo,  1  25 

Lassar-Cohn's  Practical  Urinary  Analysis.      (Lorenz.) 12mo,  1  00 

Mandel's  Hand-book  for  the  Bio-Chemical  Laboratory 12mo,  1  50 

*  Pauli's  Physical  Chemistry  in  the  Service  of  Medicine.      (Fischer.)  ..12mo,  1  25 

*  Pozzi-Escot's  Toxins  and  Venoms  and  their  Antibodies.     (Cohn.).  .  12mo,  1  00 

Rostoski's  Serum  Diagnosis.      (Bolduan.) 12mo,  1  00 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  00 

Whys  in  Pharmacy 12mo,  1  00 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.)  ..  ..8vo,  2  50 

*  Satterlee's  Outlines  of  Human  Embryology 12mo,  1  25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,  2  50 

*  Whipple's  Tyhpoid  Fever Large  12mo,  3  00 

Woodhull's  Notes  on  Military  Hygiene 16mo,  1  50 

*  Personal  Hygiene 12mo,  1  00 

Worcester  and  Atkinson's  Small  Hospitals  Establishment  and  Maintenance, 
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Hospital 12mo,  1  25 


METALLURGY. 

Betts's  Lead  Refining  by  Electrolysis 8vo,  4  00 

Bolland's  Encyclopedia  of  Founding  and  Dictionary  of  Foundry  Terms  used 

in  the  Practice  of  Moulding 12mo,  3  00 

Iron  Founder 12mo,  2  50 

Supplement 12mo,  2  50 

Douglas's  Untechnical  Addresses  on  Technical  Subjects 12mo,  1  00 

Goesel's  Minerals  and  Metals:  A  Reference  Book 16mo,  mor.  3  00 

*  Iles's  Lead-smelting 12mo,  2  50 

Johnson's    Rapid    Methods   for    the   Chemical   Analysis  of   Special   Steels, 

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Keep's  Cast  Iron 8vo,  2  50 

Le  ChateHer's  High- temperature  Measurements.     (Boudouard — Burgess.) 

12mo,  3  00 

Metcalf 's  Steel.     A  Manual  for  Steel-users 12mo.  2  00 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.).  .  12mo,  2  50 

Ruer's  Elements  of  Metallography.      (Mathewson) 8vo. 

Smith's  Materials  of  Machines 12mo,  1  00 

Tate  and  Stone's  Foundry  Practice 12mo,  2  00 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  00 

Part  I.      Non-metallic  Materials  of  Engineering,  s*ee  Civil  Engineering, 
page  9. 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.  A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  00 

West's  American  Foundry  Practice 12mo,  2  50 

Moulders'  Text  Book 12mo,  2  50 

16 


MINERALOGY. 

Baskerville's  Chemical  Elements.     (In  Preparation.). 

Boyd's  Map  of  Southwest  Virginia Pocket-book  form.  $2  00 

*  Browning's  Introduction  to  the  Rarer  Elements 8vo,  1  50 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.) 8vo,  4  00 

Butler's  Pocket  Hand-book  of  Minerals 16mo,  mor.  3  00 

Chester's  Catalogue  of  Minerals 8vo,  paper,  1  00 

Cloth,  1  25 

*  Crane's  Gold  and  Silver. 8vo,  5  00 

Dana's  First  Appendix  to  Dana's  New  "  System  of  Mineralogy  " .  .  Large  8vo,  1  00 
Dana's  Second  Appendix  to  Dana's  New  "  System  of  Mineralogy." 

Large  8vo, 

Manual  of  Mineralogy  and  Petrography 12mo,  2  00 

Minerals  and  How  to  Study  Them 12mo,  1  50 

System  of  Mineralogy Large  8vo,  half  leather,  12  50 

Text-book  of  Mineralogy 8vo,  4  00 

Douglas's  Untechnical  Addresses  on  Technical  Subjects 12mo,  1  00 

Eakle's  Mineral  Tables 8vo,  1  25 

Eckel's  Stone  and  Clay  Products  Used  in  Engineering.      (In  Preparation). 

Goesel's  Minerals  and  Metals:  A  Reference  Book 16mo,  mor.  3  00 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) 12mo,  1  25 

*  Hayes's  Handbook  for  Field  Geologists 16mo,  mor.  1  50 

Iddings's  Igneous  Rocks 8vo,  5  00 

Rock  Minerals 8vo,  5  00 

Johannsen's  Determination  of  Rock-forming  Minerals  in  Thin  Sections.  8vo, 

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17 


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19 


THIS  BOOK  IS  DT7E  ON 


STAMPED  BELOW 


184 


APR-5 


LD  21-100m.7,'33 


